Well, he might use the high - frequency sword to fight against dark creatures. Maybe he has to face a powerful dark wizard and the sword gives him an edge in the battle. He could also use it to explore hidden and dangerous places in the wizarding world that are protected by magic barriers which the sword can somehow penetrate.
He could go on adventures to discover the origin of the high - frequency sword. It might be an ancient weapon with a long - lost history. So he travels to different wizarding libraries or consults with old wizards who might know something about it. Along the way, he gets into various skirmishes where the sword proves useful, and he also makes new friends who help him in his quest.
Perhaps with the high - frequency sword, Harry Potter embarks on a mission to rescue a group of kidnapped wizards. The sword's unique ability allows him to cut through the magical bindings used by the kidnappers. He has to sneak into their stronghold, which is full of traps and guards. The sword not only helps him in combat but also in solving some of the magical puzzles that stand in his way.