не надо было этого делать

shouldn't have done that

→ не
phrase Rare #31,534
shouldn't have done that Used to say that an action in the past was unnecessary or unwise. Depending on context, it can also mean “didn't need to do that.” The subject is expressed by the dative pronoun: мне, тебе, ему, вам, etc.
RU: Мне не надо было этого делать.
EN: I shouldn't have done that.