Once you are muted, it can't be undone. However, being muted lasts for 24 hours only so you don't have to wait long before you can get to talk to your favorite model again. You can still be present and see everything in free chat or even spy on her private shows as well, but you are not allowed and even able to talk.
You should consider it as a milder form of warning to remind you to change your way of communication and behavior or you may even get banned for a month from a Model's room. It is best if you send a generous tip to the model from whose room you were muted in to show her that you mean well and still wish to be her regular guest.