Hard to tell from those pictures but the surface of the lens looks like it's chipped or melted. What power is this laser? Above a watt an acrylic lens may have begun to melt, especially if there was a bit of dust or other contamination on the lens creating a hot spot.
Ditto. As the forum visual materials scientific authority (not), I can tell you it sure appears melted to me. A lot of the cheap plastic lenses used by Chinese laser pointer manufacturers have this problem for their 1 watt laser pointers and above, but I suppose a half watt can fail that way too.
I would think if it was a plastic lens it would of melted a lot quicker??
You probably know, those 2 little divots on the lens barrel in the 2nd pic are there to unscrew the lens barrel from the host. Could be some glue that will make it a bit harder.
You need to unscrew it using maby some strong tweezers, a very fine point needle nose pliers or a home made gizmo using the 2 divots that's shown in the 2nd pic.. There are spanner tools but they will probably cost as much as the Thor laser itself.
These lasers don't have lenses in AixiZ modules, so there is no reason, or way, to use a spring. The lens is mounted in the holder that unscrews from the front of the laser. You might be able to removed it by unscrewing the lens from the housing, or it may just be held in place with a bit of glue. It's difficult to say from your photos.
Like GSS said you can unscrew it by the dimples with an icepick or similar tool or use a spanner, you should screw it out the end it's closest to and it looks like it has some Teflon tape or glue so you will have to break it loose then it will unscrew, looks like brass so you should be able to get it loose.