How to get music back on a video thats been muted?

You already stated that you used a Kesha song so #1 is not an option. So either you can prove Kesha or her label gave you permission to use it (#2) or you used it in a manner that is protected under the Fair Use Law(#3) such as commentary, criticism, news reporting, research, teaching, library archiving and scholarship, it is a parody, or de minimis(you used so little of an original work that it should not concern the owner. Like having a sample of Kesha's music) then your video violates copyright laws and you won't be getting it back.