All you can do is toss it in the Misc parts bin that you should be starting. Lol

LOL...do a careful reassembly...test to see if it all works and count your blessings when it does.

I have no idea what that pin is from. When you end up with 2-3 bins of spare/misc parts...toss them all into one big bin, shake gently, add a battery and you'll probably end up with a complete AEG.