Frustration

My Kindle stopped working a few weeks ago. From the intenet (!) I learned how to heat up the back panel with a hair dryer to soften the glue and peel the back off. Last week I took the batter out -under the heat sink in the centre here. I then put it all back together. Still not working so I ordered a new battery. Today the battery arrives, I take it apart again. But I can't find the Allen Key or screwdriver to unscrew what I screwed down last week. Frustration!!