I would not attempt to cut it. in my experience, feeding an LPS with this damage never worked with me, they never showed enough feeding response and when they try it eventually made them more "sick". Unless the good part of it is puffing up enough, avoid direct feeding.
a good Amino acid can and will help, check water parameters too. I would move it to a place where it does not touch anything, with slow gentle steady flow, less light and watch it for a few days. if it was doing better I would not dip it with anything and keep an eye on it for a while.
A general advice too, I would adjust the Calcium and Magnesium level closer to NSW too, its too high at 500 and 1500.