How can I make a hickey go away fast?

Dip a washcloth in hot water to create a warm compress (but make sure it's not so hot that it will burn you), then press it to your hickey. Hold it there for about 15 minutes and swap it out with a fresh one when it cools down. That's actually much more effective than using ice or a cold compress and I know because I've tried both. :)

Try putting vitamin K or C cream or Arnica on it which can speed up healing for a bruise (which is what a hickey is).

how can I hide it fast because I'm performing in a show tomorrow and it looks really bad

A hickey is essentially a bruise, and the coloring differs depending on the life cycle of healing it’s in, but you can color correct and conceal to cover it up. A fresh hickey has red or purple tones, which you can color correct with a green or yellow color correcting cream. Then, go in with a concealer that matches or is one shade lighter than your skin tone. Set the makeup with powder. If the hickey has progressed into a yellow/green/blue bruise, you will likely need a more peachy color corrector first, then the concealer and powder.

what if i dont have makeup

Put a Band-Aid over it or wear a turtleneck, a shirt with a collar, a scarf, or a necklace, like maybe a choker, to cover it up.