Let's talk about playing bass notes on the accordion. One thing that I would say that's really important is that you stand in front of a mirror. Not only is it important to be able to see what you're doing, but you need to feel it and see it at the same time until you get a handle of what goes on with the left hand.
Something that's helped my left hand playing has been to run scales with my left hand in every position possible. Let's start with a basic C scale, starting on the fundamental bass note line with the C. Then, circle of fifths, the next note up in the line would be G. We're going to skip that to go to the D. Moving to the counter bass row, the first row just above the C, there's your E. Back to the fundamental bass note line F. Skipping over the C to the G. Counter bass row to the A. To the B. Back to the C.
I think if you just keep running those scales over and over it really will help your left hand playing, even saying them as you go, C, D, E, F, G, A, B, C. Just doing them over and over. What's great is because the accordion is set up in the circle of fifths you can do that anywhere on the instrument, even at the other end.
I think by going over these scales you can really begin to have a grasp of what needs to happen with the left hand in your playing.