Drip acclimation is just simply putting the fish in a container (bucket, food grade plastic container, etc) make sure there is plenty of room for extra water. Take some air line tubing and an air regulating valve or you can just tie a knot in the tube. Fill the tube with water from the tank leave one end in the tank and place the other end in the fish container. Adjust the flow of water coming out to about one drip per second and leave for a while. Just keep an eye on it and after about an hour it should be good. Then just transferred the fish to the tank.
I never did it before but my pH is different pretty different from the store and congos are a little picky when it comes to pH changes. They seem happy today.