want to know how to put the 3 wires back in to the plug of the knock sensor on top of the starter

you didn't say what motor? usually wire ends are held in their plastic plugs by little tabs that stick slightly out on metal end part of wire. they get bent/smushed when ripped out. fix that and they snap back in. to know what color wire goes in which hole in plug you probably have to look at another 1 on another similar vehicle.