To unlink an account from your Bungie profile: Login to the site using a different platform account than the one you wish to unlink. Click on your icon in the top right, go to Settings, then Account Linking. Scroll down to where the platform account is listed, and click unlink. You will need to authenticate the account to finalize the action. You can then link the correct account from that same page, before proceeding to the cross-save setup page.