Business Manager lets you handle ad accounts, Instagram accounts, pages, pixels, shares audiences, page roles and more in a much more professional way.
Inside Business Manager,
go to the settings (or click here: Business Manager Settings - you may have to choose a Business if you already have stuff set up).
Find and click “Ad Accounts” in the left navigation.
Then click “Add Ad Accounts” at the top right.
You can then choose to claim an existing ad account or create a new one.