Select Sign in to the iTunes Store if you have an Apple ID/Apple Account and password. If you don't have an account, choose ...

Authorize the computer you are using. From the Account menu in the iTunes/Music app, select Authorizations > Authorize This ...

The Apple Account Card feature is coming to six more countries very soon, although it isn't available for all users yet.

For some, the migration tool has been successful in transferring iTunes and App Store purchases from being associated with one Apple Account to being attached to the preferred Apple Account.