Thats easy they just screw off / on as they are fitted with 12 mm fine thread.
Most are often secured in place with a little dap of glue, but most often not a problem, just peel off what you can and unscrew the lens, some times adding a little heat from a hairdryer make things easier if they bind a little.
You will find plenty of videos on youtube swapping lenses on action cameras, which use the same kind of lenses, the procedure are the same only taking camera housing apart to get hold on lens will be different.
My lens come care of Peau productions in the states, other in here have sourced cheaper lenses on the internet, just make sure it have a IR block filter or get a loose one you can glue on yourself.
Most loose lenses you will find are for CCTV cameras and so will not have a IR block filter as in that tupe of cameras that filter are a active one found in the mount for the lens, but you can also buy loose glass filters to glue on the back end of the lens.
If you dont use a IR block filter your footage will come off Cyan colored as sensors can pick up the IR wavelengths we humans cant see.
And thats also why the IR filter are active in CCTV cameras, cuz at night the filter disengage and the IR light of the CCTV camera come on and so you get perfect black and white night footage in pitch darkness.
New lens dont secure that with CA glue, use some mild form of glue, and for god sake make sure your focus are in the sweet spot before you secure the lens, you can do testing with the camera apart or in a car with the lens not secured properly yet,,,,, its not like it will rattle out of focus easy.
Actually my 12 mm lens in this camera are just secured with thread lock tape the same as plumbers use on pipes, just there to make the threads engage a little tighter.
I have tested my focus on this camera out of my living room window, with the camera plugged in to my TV as this camera have a HDMI out ( not all cameras have this ) And then i have aimed at a child care center on the other side of the road some 20 - 25 M away.
For focus you can also use the low resolution AV out most dashcams have and plug into your TV, or you can go by minor adjustments,,,,,, it take just a fre degrees twist of the lens to be on or off the focus sweet spot, so can take some trial and error if you have to go by it that way.
BTW, if you go fishing for a cheap lens, the really cheap ones are cheap for a reason, and there are also the ones for low resolution analog cameras to be aware off, so make sure the lens you find are a megapixel one ( 2 megapixel = 1080p )
You can use a 16 megapixel one if you like, over killing like that are no problem,, but say you had a 12 megapixel camera it would be less that optimal to use a 2 megapixel lens on that.
you might want to browse thru these 2 posts too from the mobius subforum.
https://dashcamtalk.com/forum/threads/mobius-5mp-varifocal-zoom-6-22mm-ƒ-1-6.34263/#post-406719
https://dashcamtalk.com/forum/threads/mobius-varifocal-zoom-ir.30602/