Same as any other tile job but you may need to drain the pool to do it.
I'd buy a cheap air hammer and compressor if you don't already have one or slug it out with a cold chisel and mallet. Remove all the damaged tile (might as well do it right and strip the whole perimeter of tile.. Clean up the surface with a wire brush and whatever then use a good quality modified thinset mortar to set the new tiles. Finally use a good grout to finish it off.
The price is reasonable really, considering the labor cost these days. Even if they are just removing and replacing the grout, effort is about as much, only materials are less that way. 1 foot is what; 4 tiles or 36 linear inches of grout line. $250 to drive to your house, haul out all the gear, prep the site, do some work and clean up. If that includes materials, it's a good deal. If they don't drain the pool and do it in one day, its excellent.
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