Depends on the chin rest; most I've seen have a little metal "tube" over the metal bracket on the side that you can tighten it loosen by, and the bracket is threaded. Sorry, I don't know the technical term.
I haven't met an uncomfortable one yet, but they do come in different shapes and sizes and you can always replace yours. HOW is is uncomfortable? They also sell little pillows for chin rests, too.

Pegs: by a little tube of compound called Peg Dope, about $5. Remove string and apply to peg as directed. It takes a few days or weeks to really settle in, but the stuff is awesome for slippery or worn out pegs.

Bowing technique: Spend a few dollars with a teacher to verify you are holding the bow correctly and your arm/elbow/wrist motion is correct. It'll save aches and pains and troubles down the road, and it'll really help loosen you up so that you can play better and easier.

Welcome back!