You can also read about the POWERBENDER tuning in this extract from the Introduction to the PowerBender book.
Finally, see this tuning table which shows both tunings, along with a range of other tunings for diatonic harps.
Remove the outer coverplates. Remember which one goes where and keep the screws in a safe place. On a diatonic harmonica, the upper reedplate has the blow reeds (not fully visible, beneath the reedplate) and the lower plate has the draw reeds (fully visible, on the outside of the reedplate).
If the problem is with a draw reed, examine the reed in question closely. It could be there is a tiny bit of debris or a miniscule hair jammed between the reed and the slot, almost invisible to the naked eye - that's all it can take to stop a reed working. If you can see something, carefully remove it with tweezers. If not, flick the end of the reed a few times - being careful not to bend it! Then draw on the hole - maybe the problem is now fixed? As likely as not, that is the problem.
If the problem is with a blow reed, do the same examination. You can see as much, but you might spot some obstruction. If possible, remove it with tweezers. If not, push down gently on the reed a few times, being careful not to bend it, then blow. That could be enough to dislodge any obstruction.
If neither of these fixes the problem, all is not lost: it could be because the reed gap is too small. Try blowing or drawing with VERY light breath? Does the reed sound? Then try with strong breath - does it not play? That means the end gap is too small. All you have to do is look at the adjacent reeds on either side and gently bend the reed so that its end gap looks the same size as theirs. Push down on a blow reed and lift up on a draw reed. Increasing the gap should the allow the reed to play under a strong breath. If it's still a bit sticky, increase the gap very slightly again, but don't make it big by comparison with the adjacent reeds.
Every harmonica player should be able to do these basic checks if a reed stops working. For a new harmonica, these two procedures will cure the problem 99% of the time. Assuming the problem is fixed, replace the coverplates and get playing! If not, check that you did everything thoroughly one more time. If there is still a problem after that, get in touch with us.