Lens' for fluorescent lights usually can be removed without disassembling the fixture. Try pressing you thumbs against the top of the lens while gently pulling down with the rest of your hand. It should snap out and down. Then push the lens either left or right and see if it will clear the edge ridge on one side or the other. Then just work it out.
If you do have to remove a side plate, you need to get a tamper proof screw drive the fits the 2-hole head.
Personal opinion: Looking at you pictures I wouldn't waste time repairing it. I would get an inexpensive fixture and replace it. In fact if you have to replace the ballast and lamps, the price of the material may be about the same of an inexpensive replacement.
Good luck and stay safe make sure the circuit is dead while working on it.