I used to know but it has been a decade or two and I have forgotten. I have a similar question as OP's. It is not about which airline miles that the credit card that the points will transfer to, but rather say, I have a ton of United miles... if I wish to travel on Star Alliance network, do I call the other Star Alliance airline company and transfer/use(?) to book in their system?
From the United website. I highlighted the piece I think you're interested in.
Star Alliance air travel award rules
Star Alliance awards have limited availability and are subject to capacity controls.
Unless otherwise noted, Star Alliance air travel awards may be booked on any combination of flights operated by Star Alliance members.
Most travel award itineraries may be booked at united.com. Certain travel awards may only be booked over the phone with your local United Customer Contact Center. An award booking service fee of $25 per person will apply to all bookings made over the phone, regardless of whether it is possible to be booked at united.com.
Cities and countries served by the Star Alliance partners are subject to change. Some countries listed in the award chart may not be available for award travel and other countries may become available later.
Awards ticketed less than 21 days before travel will be subject to a close-in award booking fee. Please see the Award Ticketing Options/Service Fees page for more details.
All fees are based on the status of the account holder at the time the ticket is booked.
Different award types (Saver and Standard) and cabins may be combined to create a single roundtrip award. Awards may not be combined or used with any other air travel certificate, discount coupon, premium offer or specific promotional fares.
You can also book a One-Way Award if you wish to travel one way. If you redeem your roundtrip award and only travel one-way, the unused portion of the award will be forfeited.
Two open jaws are permitted per roundtrip award. For example, you can fly from New York/Newark to London and return from Paris to Washington Dulles.
A stopover is permitted on roundtrip award travel only. One stopover is permitted, unless otherwise noted. Additional mileage may be required for Saver Awards within the continental U.S., Alaska and Canada. For travel booked on or after February 1, 2014, a stopover is permitted only on certain roundtrip itineraries. Additional mileage may be required.
Economy awards may be exchanged for a higher cabin, if available, for the difference in mileage and applicable award change fee. Travel awards may not be used in conjunction with promotional upgrades or MileagePlus® Upgrade Awards.
Travel awards are not eligible for mileage accrual with MileagePlus or any other loyalty program.
Unused or canceled MileagePlus awards may be re-deposited back to the account from which the miles were withdrawn prior to the expiration date. Award re-deposits are subject to the applicable fees. Please see the Award Ticketing Options/Service Fees page for more details.
MileagePlus travel awards have no cash value except for applicable taxes, fees and surcharges. Request for refund of taxes should be sent to refund accounting.
Unless otherwise noted, award tickets are valid one year from original date of issue. All travel must be completed within one year from date of issue. See the Interactive Award Chart for award regions.
MileagePlus members are responsible for all applicable federal inspection fees, terminal facility fees, customs and immigration fees, infant tickets (when required for children under two years of age) and any other fees or surcharges applicable to reward travel. Fees and surcharges must be paid by credit card only at the time the MileagePlus award is ticketed. Also, some international departure fees are due at the airport, payable in cash only.
Once an airline ticket is issued, the passenger name on the ticket may not be changed, and the ticket may not be used by anyone else. A name change requires that you re-deposit the award for a service fee (payable by credit card only) and request a new award in the appropriate name.
MileagePlus awards and mileage in your MileagePlus account may not be sold, bartered, traded, exchanged or purchased, except under programs fully authorized and/or sponsored by United Airlines. Awards and mileage obtained in violation of this rule will be void and confiscated. A violation of this rule may result in the termination of your MileagePlus membership and forfeiture of all mileage in your account. If a person other than the MileagePlus member or the person named on the reward attempts to use the award, it will be void and travel will be denied. Altered awards are also void. Awards deemed void will be confiscated and the mileage forfeited by the member. At the discretion of MileagePlus, actions which result in a void award may lead to membership termination and forfeiture of all mileage.
In the event of a flight delay or cancellation, you will be re-routed on the first available flight in accordance with Our United Customer Commitment. Some partners may have different policies for re-accommodation during irregular operations.
If you elect to travel in a lower class of service than specified by your award, you will not receive a mileage adjustment.
All tax liability associated with the MileagePlus program and with the receipt and use of MileagePlus awards, including income tax, is the responsibility of the customer.
If you fail to comply with the MileagePlus award rules, at United Airlines' sole discretion, you may be accommodated on a different flight than originally selected, seated in a lower class of service, denied ticketing or boarding or be subject to other action as provided under the "Mileage or Award Abuse" provision herein. Travel on United Airlines or MileagePlus airline partners is subject to the filed tariffs and standard contract of carriage of the specific carrier.