Here is a video that shows you how to tune your mbira (the mbira being tuned is a B pitch Nyamaropa tuning mbira).
Key things to remember when tuning your mbira are:
1. When the key is longer, it is lower in pitch. When it is shorter, it is higher in pitch. This refers to the length of the key beyond the bar underneath the keys.
2. When a key is loose, tap it toward the top of the board until it comes loose, then bend it down as close as possible to where it usually goes underneath the top bar over the keys. Now, tap it back into position, until the octave relationships are correct. It should no longer be loose. On an mbira with wired (as vs bolted) construction, bend the key cautiosly when tightening a key, so you don't stretch the wire and make many more keys loose!
3. Helpful tuning tools are a tabla hammer (brass, from India, with very pointed tip), a pair of pliers, a smallscrewdriver, and a small block of hardwood.