While the linking can be done only via the downloaded game on the respective platform, the unlinking function does not require entering the game. You can unlink any linked platforms via the PROS website. Here's a detailed guide on how to do that. 

• Start by signing in to your PROS account.
• Go to Account > Games.
• Press on the tab of the game you want to unlink the platform from.
• On the right side of the game page, there will be a sidebar depicting all linked platforms and a brief description of the game.
• In the bottom right corner of this panel, there will be a broken chain icon (this is the unlinking feature):

• Press on this button, then choose the platform you want to unlink:

• Please note that PROS will delete all your data for this platform, and you will lose your rewards on PROS related to this platform.
• Once the button is pressed, the platform will be unlinked. Note that it may take up to several minutes for changes to appear.