cnc laser engraver doesn't focus; help needed!

Hello,

I've had my cnc laser engraver for a couple of years now and everything went mostly smoothly.
A couple of days ago i noticed that i couldn't get my laser to properly engrave the painted aluminum cards that i was using it for.

I figured that maybe the lens got dirty, so i unscrewed the lens cap to clean the lens. I'm not sure if i didn't put the lenses back or what happened, but now the laser beam is always in the shape of a rectangle.
In the attached pictures you will see what i mean by the shape that it leaves when engraving.

What happened? Maybe i didn't put the lenses back correctly? I don't know. Any help is much appreciated!

For reference, this is not my exact machine, but something that looks very similar https://www.amazon.in/Desktop-Engrav.../dp/B089GQ8SD9

Vlad