How to contact support to fix "This Xbox Live Account is already used with another Steam account on Microsoft Flight Simulator"

This message appears when you log into Microsoft Flight Simulator for the first time on a different Steam account than the one used to purchase the game or from your account, but with a different Gamertag. 

CONTACT SUPPORT

To unlink your account, please contact our support team.

1. Click on Submit a request
2. In the drop-down menu select I need assistance with something else (Unlink Steam account, forum appeal, general question, etc...)
3. Then select "This Xbox Live Account is already used with another Steam account"
4. Fill out the contact form then click Submit.

Your ticket must include the following information:

1. Your gamertag
2. The Steam ID64 of the Steam account that is incorrectly linked
3. The Steam ID64 of the Steam account you want to link instead

To learn how to find your Steam ID, visit "How to find your Steam ID64 before contacting support"