I have built string instruments in the past, including cutting fret slots and fitting and dressing frets... but fret work is still the one job I won't tackle DIY on my favourite instruments. The couple of times I tried it didn't work out great and I didn't actually improve the problem.
If you're working with a new fretboard, all nice and flat with well cut slots, and new wire, as when building from scratch, then all is well. The trouble I found was that if you have a fretboard where the wood has shrunk, or where the factory cut a couple of the slots too wide to hold the frets snug, then you can't always tell by looking, but you find out soon enough when you try to work on the frets and nothing goes right!
My mandolin has a slightly low fret up around the 14th or 15th, but I'm not messing with it. I don't often play that far up anyhow. If I did want it fixed I'd put it in the shop. And no way would I mess with the frets on my tenor uke.
YMMV. You may find a gentle tap is all yours needs and it all goes fine.
Hope you get it sorted ok.