[944TurboHB]

I posted a little while back about my starter and pulling out some chunks of metal, the starter teeth look fine so I suspect it might be the starter ring gear or something in there. It made a very loud grinding metal noise when I would try to start the car but I can't tell if it the starter ring gear teeth because I can only see a little of it. Someone told me to take the spark plugs off and then to turn the bolt to turn the engine, but I have no idea where this bolt is or why I would need to pull the spark plugs. Could someone please tell me where to find this thing that will let me turn the engine without starting it so I can find out if I need to replace the ring gear? Thanks. What I pulled out by the way was a broken piece of what seems to be a polished metal tube, doesn't look like teeth or anything.