To register Overwatch 2 on FACEIT, you're required to have a Blizzard account as well as a FACEIT account.
Your Blizzard account is required to be; In good standing, have had Competitive games played on PC within the past 2 Seasons of Overwatch and you need to have completed the tutorial in order to have access to the FACEIT lobbies.
Once both accounts have been created, you will be directed to a page where you can choose which of the supported titles you would like to register. If you are a returning user with other games registered, you will see the option to connect a new game in the top left corner of the homepage.
After selecting Overwatch 2, you will be prompted to log in with your Blizzard account.
Click on the Connect Blizzard button and sign in with your Battle.net account.
Please note - Once an account is linked, you cannot unlink it or link any additional Blizzard accounts to your FACEIT account.