Hey there,
If Step 2 indicates that ''your Steam/Xbox account is already linked to another Twitch account'', please locate the corresponding Twitch account. We currently cannot unlink your Twitch account based on the Steam/Xbox account.
If you can log in to the corresponding Twitch account, click the "Unlink" button in Step 2 to unlink it.
If you cannot log in to the corresponding Twitch account, please contact Twitch for assistance.
Thanks for your understanding and support!
Landomando6560