Giving a FW dip would not IMO be beneficial to an infection. You shouldn't give a FW dip for an "unidentified " problem> While it may be harmless if properly done, it can finish the little guy off also.
To do a FW dip:
Take some RO water, dechlorinated tap is OK, but I wouldnt use it myself. Just go to wally world and buy a jug of it. enough to at least completly submerge the fish in the container you want to use. Besure to pick a container that isn,t contaminated or wont be a problem if it stains blue. Adjust the chemistry in the water to match the tank water in temperature AND PH. Adjust up or down as needed. It is VERY important to match these paramters. Now then add a couple/few drops of Methylene Blue, just enough to color the water blue.
Not a big deal if you get it a little dark, but you dont want pale blue anyways. Catch the fish, preferably with something other than a net. But if you have to... Place the fish in the bath for 5 minutes, now BE AT THE STANDBY! Do not leave the fish alone, watch closely, be ready to net him.
Leave the fish in the bath for 5 minutes. Some say you can go much longer, but I never have, nor would, Dont be alarmed if the fish lays on it's side, starts swimming a little panicky, changes colors or gets polka dots.
Leave him in for the full 5 min. If he startsto look like hes going to jump out, thats another story there, remove him from the FW dip immediatly. After the 5 min is up, net the fish and return to the tank from which he came.