Tokyo Mauri Glock 26 advance
 

http://profishop.sk/catus/images/g26a_60725.jpg

This is a GBB, and as u can see, the upper portion has two parts. When firing, after a few shoot, the front part becomes loose and falls off. I have no idea how to fix it and thinking of using super glue and forcing it to stick.

The front part of the "compensator"? If so, it's held on by a hex screw from underneath. Remove the slide by removing the mag, cocking the gun, pull down and hold the tabs just above the trigger and push the slide forward and off. You now have access to the screw.

I removed it, but I am unsure how to work the screw. Am I suppose to turn it so it sticks out?

No turn it in to tighten it up. Be careful though as the part is just plastic and you can easily strip it. Push the "compesator" part on as far as it will go, it seats very close to the slide. Don't push too hard as it only goes so far, then tighten up the screw. If it won't tighten, it's stripped and you'll either have to get a new "compansator" (good luck with that one) or a slightly larger screw.