How do I reset Camera and Microphone permission on macOS Mojave?

I'm using macOS Mojave and I want to use my camera and microphone to make a New Movie Recording in QuickTime Player. But when I try it gives me this error. > QuickTime Player is not authorized to access the microphone. I looked in System Preferences but the list is empty, and there's no + plus button for me to add an app, and I can't drag apps into the list. I think maybe this came up once before and I clicked Don't Allow. Now I can't get this prompt to come up again. How can I reset permissions so that the prompt comes back?