HELP HELP HELP!!! how do i fix the J on on my dell insprion 1521?

i popped off some of my keys to clean underneath them and now i cannot get the J on back on. i dont even know how to explain it anymore than that. i have all the peices and everything. i just want it back on. and also my underscore on is on but the top of it kind of sticks up. please help if you can. thank you!