Upper one of the two is the inspection port to see crankshaft rotor markings. Lower one of those two is the cover for the crankshaft rotor. There's a nut under it that you use to turn the engine with. You look thru the upper one for markings that tell you when engine is supposed to be TDC. Won't find in owners manual but will be in maintenance manual (does not come with bike) around section regarding checking valve lash. Definitely leave alone unless you have a specific reason for them off.