Mechanic having benefited from better training (6)
I believe the answer is:
fitter
'mechanic' is the definition.
(I've seen this before)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for fitter that I've seen before include "Tradesman being in better shape" , "less likely to feel fatigue" , "to get in better shape" , "Worker assembling machinery - more healthy" , "Mechanic" .)