Clean or replace aerators in Kohler 1261404-VS spray head?
Did you check the other end of the hose for clogs? I didn't find any parts listed for that model number so I think the spray head is the part. Try soaking the head in some CLR and then back wash it and see if it helps. I've worked on a lot of Kohler products and many of them are not made to be disassembled. The ones I did get apart were so scratched up I just replaced them.