Like I do for the top, I use a thin plastic guitar pick to wedge between the plastic cap and metal case. Once it’s in, turn the pick horizontal (same as the cap) and work it around until you can get your fingernails under it. Also, I believe this cap is made to go on only one way, so maybe mark which edge is front or back
The battery is a tight fit, and if the new battery doesn’t exactly match the size and shape of the original, it simply won’t fit. It has to nestle under the headphone board without putting force on it. Also it’s very important to wrap the battery wires around and out of the way in the same fashion as the original so that they don’t cause a problem when sliding the board assembly back into the body.
As others have said, do NOT pull up on the orange ribbon cable itself, because it will easily break off of the clip that’s attached to it underneath, and your click wheel will be ruined. Use a small flat screwdriver to gently and gradually pry out the white plastic plug by pushing on one side then the other, rocking it out.
This is possibly the hardest part of this job for me. Getting this metal spring clip out without damaging the ribbon cable that’s right under one side is tricky. Take your time and use care to avoid touching the cable.
Don’t use any kind of metal tool to get these plastic caps off. Metal on metal will scratch up the body. I use a thin guitar pick, work it in between the cap and case, then turn it horizontal and slide around enough until you can use your fingernail to pull the cap the rest of the way off. Don’t be aggressive and break off the little fingers on the bottom side of the cap.