Ok, so I was greasing my chain and had asked my girlfriend to spin the wheel for me. I didn't really notice but she had been turning the wheel the wrong way and when i switched gears my chain derailed. Somehow when this happened the guard between my gears and my spokes on my rear wheel came loose. Now when i pedal it makes an annoying noise.

I've never looked at this part with any real consideration so I'm not really sure if its broken or if its just come loose or what it is suppose to look like if it isn't broken. I was wondering if this is something I can quickly fix because of something ive overlooked or if i need to replace it.

The part is just a clear plastic plate, between the gears and the spokes. The plate has four little nubs on the spoke side that are irregular as if there may have been something there, that broke off and, that might have held it in place.

Thanks for the help in advance