When I try to switch the rear derailleur to the highest gear, it will go off the into the grove. A friend tells me to turn the “H” a couple of turns (clockwise), but it does not seem to work. When I looked up online, I found a very good video that gives the basic.

Here are the main steps to adjust:

	
If the derailleur hanger is clearly bent, it needs to be fixed first. Derailleur Hanger Alignment
	
There are three screws: L, H, and B on the derailleur, H is for the smallest gear and L is for the largest gear and B is for the chain gap
	
There are also bearing adjustment screws for tightening the cable.
	
Use the largest front chain ring if it has multiple rings 
	
And, switch to the smallest rear ring
	
Locate the bearing adjust screw and turn it clockwise to expand the cable
	
Locate the "H"-limit screw
	
Make sure the chain is on the outermost gear on the rear and slight noise can be heard when moving the chain.
	
Turn the H-screw 1/4 turn (counter clockwise) at a time until no noise is heard

Here are my updated note

Put the chain on the outmost gear on both front and back.
Push more on the shifter out to max the position.
Turn the bearing adjuster clockwise a few turns.
H: clockwise makes it inwards; counter-clockwise makes it outwards.
Tighten the H adjuster screw until hearing the noise
Slowly turn the H screw counter clockwise, 1/4 turn at a time until no noise comes out.

Adjusting the index

Put the front in the middle gear, 
Adjust the bearing screws.

My friend recommended Park Tool