Resolves living ppl's regrets

That's an extremely interesting question...(and most of the ones I've seen involve ghosts and death tbh).

At a guess, I'd say a drama like Knight Flower. I haven't seen it but from what I understand the FL sneaks out to secretly resolve the issues of those around her. You'd be looking at plotlines similar to "Touched By an Angel" (a very old US series I only know of thanks to my mother as it's something she watched from time to time when she was younger).

Possibly....

 Order of the Sommelier? The leads run a bar where the drinks allow people to resolve issues of their past lives (they're reincarnated and alive in the present).

8.2 Byo no Hosoku? ML's cooking helps couples with their problems. It's a BL.