zinkiew,
Why don't you go to the "Screen Protector Mfg" web site and see what they say about removing the residue mark. Most all S. P. sites have a section on how to clean the screen when you take the protector off.
That said have you tried a damp soft cloth?
You can also try a piece of "Scotch Tape"... press the sticky side of the tape on the bubble mark and then lift it off. You may have to do it several times to get it all.
Their may be some solvents like alcohol that will remove the mark if it is glue residue from the protector. But make sure you check with Apple before you use any solvents. Some solvents may attack the Oleophobic coating on the iPhone screen.
You can also Google for a solution to your problem. I have seen several "How to" articles to deal with the issue you are having.
Just so you don't do something to make things worse I will repeat my caveat - Check with Apple before you use anything but a damp soft cloth.