hello, on accordions that have 3 rows of chords the last row on the outside of the body is in fact a diminished fifth. This allows you to play diminished chords. I won't go into the details of the harmony. So to make a diminished chord you just have to play the 7th chord which are one row down. Example to make a diminished C play the F7. For your request of the diminished A sharp (which is equal to Bb) play a button lower or Eb 7th. Or if it is too far for your score any note of the same vertical rank as the Eb, i.e. C7, Eb7, F sharp7 or A7. My explanation is of course only valid on accordions with 3 rows of chords. If you have any other questions, please do not hesitate to contact me. Jean-Yves Sixt from Switzerland