FW dips do not really "treat" ich. At best, it can knock off some parasites, but certainly not all. In my view, its far more stressful and hazardous, especially for someone who does not know how to do it, then whatever small advantage you might obtain from the procedure.
Treat ich with hyposalinity. Best choice. You will need to constantly babysit the QT during treatment, since its not cycled.
The FW procedure is: Using RO water in a dedicated container that is aerated, you bring the pH and the temp up to the exact same parameters of your display tank (or whatever conditions the fish are living in). You bath the fish in this for 3-5 mins. Expect to see extreme behavior, and shock.
After the procedure, return the fish to the QT.
Unless the fish are in dire conditions with ich, and at risk of death, I'd hold off.