my iphone keeps asking for the password of an old apple id account. How can I stop that? I don

Check the App Store and iTunes Store to see if there are any updates for apps/purchases. A request for another Apple ID password is often caused by updates to apps/purchases that were made when using the other ID. Those purchases are tied to the other ID and can't be transferred. One option is to delete the apps/purchases made by the other ID and download them using the new ID if desired. If necessary, check your purchases history to see which apps/purchases weren’t made by the current ID. 

Purchase History Review

You are welcome. Can you sign out of the old ID? See if anything here helps.

Settings - Update Apple ID Settings When It Won’t Go Away

Settings - Update Apple ID Settings When It Won’t Go Away (2)

You are welcome.