Q: Change apple id for downloaded apps

Hi,

I have the following problem:

When I set up my phone a former colleague helped me to install everything and downloaded some apps while signed in with his apple id. Now I learned that every purchase in the app store is tied to the apple id which downloaded it.

And so it happens that when I try to update Whats App it's asking me for that colleagues password. I'm not working in that company anymore and can't contact him as he changed the company too and I don't have any conact details. I'm using my own apple id for quite some time now. Is there a way to reassign all apps/purchases to my current apple id.

I can't even create a backup of Whats App as it claims to be outdated. Deleting it isn't option because I don't want to lose my data.

Any help appreciated!