If a channel is linked to a Brand Account, multiple people can manage it from their Google Account. You don't need a separate username or password to manage YouTube channels with a Brand Account.
First, check if your channel is already connected to a Brand Account:
Go to www.myaccount.google.com/brandaccounts. You may need to sign in first.
Check under "Your Brand Accounts" to find your associated Brand Accounts.
- Check that you're using the right account by selecting your profile picture in the top right if you don’t find anything listed.