Question: “In a Buddhist context how to deal with regret?”
In the simplest way I can put it: Get over it!
Regretting anything means regretting the past, the past that you cannot go back to and change, so why dwell on it? Who are you helping or benefitting by being so worried about it? Certainly not you and certainly not the environment you’re neglecting because you’re so worried about whatever it is you regret.
This is literally what I tell myself when I do something that I wished I would of done/said differently: “Damnit. F**k it. It already happened so who cares?!” The only thing you can do to “change” anything is to try to change the outcome of whatever it is you did/said wrong. So if you’d said or did something to hurt someone’s feelings, missed something, etc etc., do something to make up for it.
Otherwise, you can attempt to build a time machine and go back and try to change history. Since that obviously won’t be happening anytime soon, we can at least try to alleviate the outcome of the regret for the future.
Smile and be well!