Chosen Solution
I am having trouble using the ifixit kit to successfully open the GS6. The adhesive holding the rear glass is not loosening up for me to be able to remove it using the provided suction cup. Any ideas?
As Daniel has suggested, I would use a Blow Dryer or a heat gun to heat the back. Heat it up just to the point of it being uncomfortably warm to the touch but not so hot that it burns you.
Please if you’re unsure of doing it with a hair dryer or heat gun DON’T DO IT! iFixit has an awesome tool that works great for this iOpener
You need heat. Without heat you will not get it off.