Use of words varies, in English at least. There is no official (EASA) definition of any category of aircraft maintenance worker below "Licensed AME". Some people/countries refer to "mechanics" meaning unlicensed staff, while "engineers" refers to the licensed elite, ie AMEs. But in the USA a "mechanic" has a license, and can certify.
"Fitter" probably has its origins in the military, English-speaking of coourse.
Probably the best description is unlicensed fitter or mechanic.
If anyone has a better-informed answer I would be happy to defer!