how to transfer apple app to another accoun

You can't move purchases from one account to another.

but you can move data. This article can be useful for that:

Archive or make copies of the information you store in iCloud – Apple Support

And you can use family sharing to share some of the purchases. You need to have the old apple ID in a family sharing group.

Share App Store, iTunes Store, and Apple Books purchases with Family Sharing - Apple Support

My advice would be to keep the apple ID you have purchases on, and move content from the other apple ID if that does not have purchases, And you can change the apple ID name of that account. Or use family sharing to share some of the purchases.

Change your Apple ID - Apple Support

Good luck!