How do I fix a broken rear main seal

We dont' have much for that car, but if it's a rope seal go to an auto parts store and see if they have a puller for rope seals. It's also called a chinese bandit. You have to drop the oil pan then take the rear main cap off and put tool into seal and pull out also use tool to install the new one. That is on the upper on e only. The bottomone your beat it back in with a round object and make sure to cut them off even withblock/cap mating surface. Then apply a little silicone to that seal area when you put it back together. If they are rubber, then just drive the old oen out with a punch screwdriver til you can grab it. But use the silicone on install then retorque the cap. Retoraue cap to about 85ft. Lb. Install reverse order. If oil pan gasket not one piece put siliicone on corners.

Sounds like there is more damage than you suspect. Due to what you have told me here, just do yourself a favor and pull the engine out and repair it like that. The reason being is if it's messed up to much the engine will already be out and can be taken to a pro like a rebuilder. Sounds like your friend didn't help you much at all except cost you more money.