You'll need a flat surface. Some very fine wet and dry paper. 2000 for finishing and a dust mask. Also a willingness to chuck it in the bin when you're covered in dust and it still won't play.
Lots of videos on utube to get you going.
There is a black 2 part epoxy that costs almost as much as a new mouthpiece that you could fill the chips in with and then file and sand it back to the way it was originally. I have done this to fill in bite marks. On a Yamaha 4C you have to ask yourself if it is worth it.
I refaced a 4c once...just because I could. I didnt try to play with chambers or make it sound different. It still sounded like a sleepy 4c. Go for it. If it goes bad its just a cup of coffee.
If it goes well dont think yourself too clever and start working on a really high end piece. When I knew just enough to be dangerous I wrecked an expensive mouthpiece. Years later I knew enough to bring it back from the grave. I ended up selling it to a pro who fell in love with it. It didnt stop me from having felt really stupid whenever I saw the piece for a good while.
While looking for an alto piece I tried a 7C. Well finished. Very easy blow. Predictable response. Honest tone. Blends well. Loud enough to solo when pushed. Not fussy about reeds at all.
A cheap versatile stepping stone to see how you get on with a bigger tip opening.
I can see why experienced players are unimpressed though.