Q: Old laptop won't forget iPhone (not selling it)

Hello, thanks in advance for any help.

I have always had a Macbook Pro, and currently have an iPhone 6s Plus. The Macbook pro is starting to die, and I have also got an iMac. Currently, I sync the iPhone with the Macbook and there have never been any issues.

What I am trying to do is now use the iMac with the iPhone, instead of the Macbook. I have moved all of the content onto the new iMac, got the playlists back as they should be. Everything is basically identical (although the iMac seems to have all apps I've ever downloaded).

When I connect the iPhone to the iMac, I can sync the music, TV shows, movies, photos etc. But the phone still thinks that the old Macbook Pro is being used for Apps. On top of this, the Macbook still shows the small iPhone symbol (showing that it is connected), which means that it is still showing on that computer.

Basically the question is, why will the Macbook Pro not forget the iPhone, now that it is synced with a new laptop.

I have tried removing the iPhone from my devices, I have deleted the old backups etc, and followed all other threads I can find.

I do have my own reasons for doing this, the laptop and iMac are to be used for different reasons going forward, so do not want the iPhone linking up with the Macbook in any way.

Many thanks.