Hello and welcome to FF! Mixing fish with ADF is not a good idea since the fish eat way faster than the frogs and you will stress all of them trying to isolate frogs to feed.

You could try to isolate frog inside a large net and see if it will eat in there. If that does not work; would then tranfer the underweight frog to a tank by itself and keep it there until it eats well and looks normal. Good luck !