Thumb Air Valve and reed switches

On any concertina will be some kind of air valve that allows you to draw or press the concertina to fill or expel air from the bellows without making any sound through the reeds.

This is very important: Never force the bellows open or closed without using the air valve (or by playing).  Forcing air out can damage the seal of the bellows.

Use the thumb air valve:

The air valve is also used to inflate or deflate the bellows while playing when you run out of room drawing or pressing and still have more notes to play in that direction.

In addition to the air valve, there also may be an octave switch or several switches that will enable different combinations of reed chambers to be open.  In the case of the Star Streamline concertina shown, there is just an octave key lever that will block the lower octave reeds of the right side - I think it's called the "Hi-Lo" switch.  Other designs of "Triple" and "Quad" reed concertinas could have 5 or 8 switches that will open or block different combinations of reeds, with names like Master (all reeds), Musette (3 reeds), Bandonion (2 reeds: low and middle), Clarinet (1 middle), or Bassoon (1 low).