This week, Apple quietly gave iPhone and iPad users a long-awaited new ability — for the first time, you can migrate app purchases (such as music, movies and books) from one Apple Account to another.
This is a big deal for people with two separate Apple Accounts, using one as a primary tied to their iCloud account and one as a secondary for in-app purchases. This way, you can consolidate the two and just make your life that much easier.
There is a little bit of a catch, however. You can only migrate app purchases from the secondary to the primary Apple Account, and not vice versa. Also, the secondary Apple Account can’t be part of a Family Sharing group.

How to migrate purchases between Apple Accounts
As explained on an Apple Support page, there are a couple things you need to know and do before migrating purchases.
First, you need to know the email address (or phone number) and password for both accounts. You must then sign into both accounts on the same iPhone or iPad, which you can do in Settings.