Sorry Irina,
I'm only seeing this now.
Coming from a flute perspective, you're never going to be able to get exactly the same sort of rolls on the concertina, as you could get previously on the concert flute. In some cases the rolls will not be as good as those on the flute, but in other cases the rolls can be very much better.
Have a bash at this one, it might be a little bit different to what you'd expect, and see how you get on.
I like to use my 2nd playing finger for the first B, and glance it upwards, to replace it with your 1st playing finger, again on B. (You could do it the other way around, but at least, this way, your fingers are back in the "home" position.)
Regards, John.