How do I reassign a variable?

in the space shooter tutorial, on the creating/shooting shots video. Everytime I run the game and try to shoot a laser, it just pauses the game and gives me this error:
“MissingReferenceConception; The variable shot of PlayerController doesn’t exist anymore.”
I clicked on it and it took me to one specific line in the PlayerController code, which was:
“Instantiate(shot, shotSpawn.position, shotSpawn.rotation);”
It suggests reassigning the shot variable, but I don’t know how to really do that so…

shot is a GameObject, probably a public one, so you could assign it in the inspector on which gameobject you put this script on. You should put a prefab on shot variable so it can instantiate it from the source.