Working on your own harps is a skills all harmonica players should learn. There are plenty of sites like www.tenhole.com (Thanks Tinus) they tell you everything you need to know about tuning harps.
It only takes a few hours and a few harp to pick up enough skill and experience to be able to do aynthing to a harp in 20 minutes. And if you break one they're only $20 bucks or less. No worries.
Peace and music, Dave