I’d second what tennosea says, to stick with the refeeding, with time and patience weight distribution evens out.
I wouldn’t worry about exercise, you may find that just refeeding helps build back your muscles without much exercise. You have two things going for your in this regard, you are young and male!
If you really want to exercise, perhaps something light like a minimal kettlebell workout. I have found kettlebells to be the ultimate less is more workout. Just one short session a week can be enough for me (and I’m a girl so don’t build muscle easily!).