H Ian
Have you still got the instructions if so look at fine tuning In this section you can cancel reverse and you may have done that whilst playing about with it.
have you checked that the reverse is active ? after you have done the part you have done so far , in the fine tuning section of the instructions there is a part that you have to press the green button FOUR times and then push down on your lever and then back to the middle ,This should activate your reverse .
Hope this helps ,its a fiddly job with only two hands ,if you don’t manage go to your local club and someone there will help
Ducky