(Experienced harmonica players may think this tip is beginner-ish)
Blow bending is…weird.
To the uninitiated, Blow bending is when you bend the notes on holes 7,8,9, &10, but by blowing instead of drawing air.
The challenging part is that blow bending requires a different embrochure than draw bends, and is almost as frustrating to learn. Tougue placements for blow bending is much more fine than with draw bending.
My tip is to practice blow bends on a ‘G’ harp. This is much easier to hit the bent notes on, in part because of its low tuning.
Once you get the idea of how to do a blow bend, the other keys become much easier.