Byo Soa Lightsource lens blurry

Hello,

I am new to this forum but I have a particulair problem

I have bought a Byo Soa microscope long time ago but the lens of the light emmiter is getting blurry. This gives a repeating patern in the the oculair lens which is clean.

I tried to polish it with fibre cloth but nothing happened.
Does any have a clue how to fix this?

Lens is not glass but plastic. I guess it overheated, with blurryness as a result.