wing it

to improvise; to do something extemporaneously. I lost my lecture notes, so I had to wing it. Don't worry. Just go out there and wing it.

to invent a way to deal with a situation you are not prepared for I didn't have time to write a speech, so I just had to wing it in front of a large audience. Some actors can wing it, others go completely silent when something happens on stage that isn't supposed to happen.

to do the best that you can in a situation that you are not prepared for I hadn't had time to prepare the talk so I just had to wing it.

Improvise, as in The interviewer had not read the author's book; he was just winging it. This expression comes from the theater, where it alludes to an actor studying his part in the wings (the areas to either side of the stage) because he has been suddenly called on to replace another. First recorded in 1885, it eventually was extended to other kinds of improvisation based on unpreparedness.

To improvise: I hadn't prepared for the interview, so I had to wing it.