If you're just QT the fish before you place it in the tank then all you need to do is place some rock or pvc in the tank, so the fish will have some place to hide. The a heater and some thing to move the water around, like a small filter or power head. water surface breakage is important.
If the fish has something then you need to treat it. Depending on what it has you can then pick the proper treatment.
Monitor the parameters in the Qt daily, as well stay on top of water changes, because the small tank with no established bacteria will quickly become elevated in ammonia and nitrite. I used the established water in my qt as well, a piece of my filter pad in the water, but it still had elevated nitrite levels.