The springloaded button that pops up to change the tailwheel from a shopping cart wheel to a steerable tailwheel has been depressed and not popped up. I suppose I could hit it with a stick driven by a hammer and hope it pops up again, but how does one disassemble the collar to fix the problem forever (perhaps the spring is broken? for now the tailwheel is always out of detente and swivels at will. I just stumbled on it so doesn't seem to have made much difference. (my plane has always been unresponsive in steering).