Place a compass next to the magnet you intend to use to repel the strong magnet. The end of the needle that usually points toward the north pole of the planet will point to the south pole on the magnet.
Place the compass next to the magnet you'd like to repel to determine the location of its south pole.
Move your magnet close to the magnet you'd like to repel. Line it up so that either of the same poles will be against each other, either the north pole against the north pole or the south pole against the south pole. Once the poles are lined up properly, your magnet will repel the other magnet.