Have a look at this link to the service manual. Yep you can see in pics how to get into your OVF area. Don't forget to download or right down the 4 digit number to view it in Adobe PDF Reader.
Downloads
To make life easy working with your camera there is nothing more important than the proper tools. In this case its just a number 0 Philip screw driver. Buy a decent quality kit or screw driver. Better with a magnetized head! Then go to it. Not much you can hurt in that area.
Do keep small screws away from the unit if opened as your K100 has strong magnets for the SR system. Now that would not be fun