Why can't I answer calls with my AirPods on iPhone 12 miini?

I have been given Apple AirPods 2031 2nd generation I believe they are.

I can listen to music and the like from the phone but I cannot answer an incoming call. I see notification that there is a call but all attempts to answer it always goes to the phone, not the pods?

How do I set this up please?

[Re-Titled by Moderator]