Watch this video -
To sum up what you watched -
Open StreamFab and a regular browser and pull up YouTube in both. Knowing what needs to be done I'd say use either Chrome or Edge for the browser and make sure sync is on.
In the browser, if it shows your user account in the upper right, Sign out. Then Sign in to the browser. Go over to StreamFab and click the Sign in and it will change to your user account.