Goethe is the German poet who once said: What your eyes don’t know, they cannot see. (Was das Auge nicht kennt, sieht es nicht.) It’s undoubtly true: You know when you travel around in strange cultures, you tend to ignore something (by accident), because you haven’t seen it. However, the Gürtel is simply a waistbelt.
So what’s the poet to do with the waistbelt? Basicly nothing~~~ It’s all about pronunciation. Since the vowels are formed basicly by the tongue in the oral cavity, the solution is here to focus on the position of the tongue: if it sounds like ü, you just have to go down a bit; if it sounds like o then, please go forward a bit. Then you will have the ö.
You can have a look here at my diagram.
Be patient! I know it’s not easy. Good luck!