In order to create a Google Brand Account, you used to start by creating a Google+ page for your business and then you could associate a personal Youtube channel with that brand account. Now that google+ has shut down, you cannot create a brand account through Google Plus Pages.
Here’s how to do it.
Click on this link to create a new brand account:
To associate your existing youtube channel with this new brand account, switch to your personal youtube channel via the user menu on top right of youtube. Then click on this link: https://www.youtube.com/account_advanced
On that page, click the link that says Associate with a Brand Account. Follow that page to switch your youtube channel from being connected to your personal account and connect it with your new brand account. Your videos will stay intact.
You can see all your new Brand accounts here:
If you click on a brand account, you can add users and owners to access that account.