Sewing Machine Stitch Length

[unicorn]

my sewing machine stitch length doesnt work I know it can be fixed by a screw in top but dont know where if anyone can help

[murraymints]

model ?

[Mosaic]

There are several variables to take into account: type of thread, type of fabric, type of needle.
A thread that is too fine (budget thread) will often skip, especially on slippery fabric.
You also need to use similar weight thread in both feeds, bobbin and top feed.
So try fiddling with those.
Stitch length is usually controlled by a dial with numbers on it, but these are in various locations on different machines.
I think you will be altering the tension of the upper thread feed if you 'turn a screw; with a scredriver, that is.