My built in camera is not working on my macbook pro

Unless you have some third party software installed that is affecting the camera most likely you have a hardware issue that will need to be repaired by Apple or an Apple Authorized Service Provider.

Try rebooting your laptop.

Try reinstalling macOS over top of itself. If that does not work, then perform a clean install of macOS by first erasing the whole physical drive before installing macOS. Test the camera before migrating or restoring from a backup and before installing any third party software. Make sure to have a good backup before performing the clean install.

https://support.apple.com/kb/HT201314