Here are wheatstones instructions for the english concertina by Alf Edwards[accompanist for Bert lloyd].
The bellows is moved by the right hand. It should be moved steadily and as much as possible in a straight line, taking care not to turn or twist the instrument.It is preferable to open the bellows to the full extent and then close it without making a break in the sound,but above all avoid changing direction in the middle of phrases.Study the changes the same as if a person were taking a breath in singing;the best places for changing direction, of course are at the end of phrases and during rests.
         Fingering and touch.
   a staccato passage is played by tapping the keys smartly allowing the fingers to rebound. the variation of tone loud and soft is managed by the bellows.
      things to avoid.
vibrato, swelling up and down on each note.2 loud playing of close chords only widespread chords should be played loudly 3 when force is required it must only be obtained by accumulating notes either in octaves or harmony.
    these are not my views[ although I agreewith some of it].but ALF EDWARDS WAS AN ACCOMPLISHED PLAYER,and he has a slightly different perspective from the salvation army tutor., on bellows control.
and again some of it may be useful.Dick Miles