Delete synced photos from iPad

A friend of mine lend me his iPad for a project in order to use it as a second display via sidecar.

This is his everyday iPad, with all his photos in it.

I changed the Apple ID on the iPad in order to use sidecar with my Mac not realizing that our photo libraries were going to sync!

Now, all my photos are mixed with his photos in his iPad and and the same thing in my Mac.

Is there a way to delete all of his photos from my Mac, and my photos from his iPad?

thank you for your answers.