What should I do???!??

hello im a first time outdoor grower and during about 2 weeks one of my plants had an insect attack and due to my ignorance I reacted with it with nuitrients and nute burned acoulpe leaves. Iv heard the best thing to do with a damaged leaf like this is to pluck it off. what should i do in this situation? btw the first bottom round leaves that sprouted have shrivelled up on all of my plants is this ok? thankyou for you help