If the goal is prevention without the fish showing actual symptoms I would only do one dip - the one at arrival.
It is done easily:
1. take the fish out of the bag and place them into a container. Take just as much water from the bag as is needed for the fish to swim. in the container. Ideally you use a graduated container or one you have metered out and marked yourself so you know which volume you have at a certain fill level.
2. drip acclimate the fish to your QT water until you reach the mark. With my standard container it's 1/2 gallon, but you may use whatever is required for your fish.
3. if not already in it, add an air bubbler or small pump and then add the appropriate dose of formalin (20 drops per gallon). Keep an eye on the fish during the bath and pull them if they show signs of distress.
4. after 30 to 50 minutes (I always go 45) move the fish over to the QT tank used for tank transfer.
