It is a working GMT hand, you pull out the crown to the "set date" position, then turn it CCW, instead to set the GMT time.
One warning though, the GMT hacked A7750 movement has been the subject of quite a few threads by the experts in a few forums, and many believe that is very prone to breakdown. This movement is used in most GMT watches with seconds at "9" and a functional GMT hand, not just the 088.