It’s about tandem flare with heavy student.

I would like to know, if I take tandem jump, and the exit weight is 500 pounds, How much power do I need to land flare

Lots of arm muscle.

May I suggest training in the gymnasium 3 or 4 times per week to include chin-ups, curls, push-ups, parallel-bar dips, etc.

Technique also helps a lot.

Personally, I like to pull toggles to shoulder level, then rotate my elbows up so that I am using more muscles (pectorals, latimus dorsi, trapesius, etc. to finish the bottom half of the flare.

Enough power to not hit the ground and get injured or die.  It would be safe to guess you'd need more than a 300lb exit weight.   But really it's technique.

I have done 1000s at that weight / wing loading - no problem at all.