How to adjust round shower cup door? It is uneven on the bottom and I can't find any approach...

It is uneven on the bottom and I can't find any approach to adjust it. doesn't seem to be any screw or shims or anything.
Thermostatic Radiator Valves?
Answers:    If you cannot adjust the wheels within any way consequently you can even this out by adjusting the track that the wheel run in at the top usually these tracks are not fastened they freshly lay on the end pieces so you could move up the end obligingly (this works better if you can remove the doors first)and put a shim of some sort in at hand to get the adjustment you stipulation on the end you inevitability adjusted.