Ryobi 990r Weed Whacker

Does anyone have one of these that they have repaired themselves. I took it to a repair shop and they told me mice had eaten the ignition module, the part is no longer available, therefore it can't be fixed. I can see damage to the wire that attaches to the spark plug, but I'm steady taking this thing apart to look at the actual part, in hopes that the wire only can be replaced.

I'm down to taking the starter housing off, but I can't figure out how to get it off. There is a thin plate with a notch that says off and an arrow pointing to the right. What tool do I use to move this plate.

Any assistance would be appreciated.

Judy

PS No I don't know what I'm doing, I've never worked on yard equipment before.