I looked at the link Juliasb provided but couldn't tell enough from what I can see.
Not all machines have feed dogs you can drop, my old vintage machine had a "darning plate" to achieve the same thing. It's metal and has slits for the feed dogs but they don't go above the metal, then it has two holes in the bobbin cover the darning plate hooks into. Unfortunately for me, the darning plate was lost before I got the machine and so for some 20-30 years of quilting everything I did was feed dog engaged.
My current Cheapo Brother which is working while my expensive machine needs to go to the shop is very low end, it doesn't even have adjustable stitch length, just a dial for "shorter" or "longer" options -- not to make them shorter or longer but just to switch to their preset lengths.