If you unscrew the light lens with water in the tub, you will have a problem. There is a trim ring which can be removed with water in, but I bet that's not what you mean.
If the light lens needs cleaning, open the motor compartment door, find the LED assembly, and gently pull it free. It is a press fit into three anchors, no tools needed. Once it has been pulled free, you can clean the lens from the backside. Once this is done, you shouldn't have to do it again - I have no idea how it got dirty in the first place.
Once you have it nice and clean - a damp cloth should suffice - press the LED assembly back in place, test it, and then close the motor compartment door.