Fret level work
This is performed to remove scratchy, unlevel, pitted, and non-performing frets.A fret level is usually accessed by a luthier.
You want to make sure there’s lots of fret height to perform this work properly.
If you have deep pits in the frets you might be removing too much of the fret, so the end result would be very low frets. If you have plenty of fret height, the objective is to remove as little fret surface as needed, ( but still removing pits etc,) other things can be removed at the same time such as sharp fret ends and other unwanted problems.
After achieving perfectly leveled frets, they must then be crowned, ( this means the tops get rounded), after that they must be polished. So as you can see this is a multi-step procedure which is very precise work and done with lots TLC!