how to leave a group

I have tried to join privet groups that done seem to be run by anyone now . when I go to the group to try and leave I get. a message saying Your membership is pending approval
Please be patient during this process

I think waiting 2 to 3 years is very patient ,I would like to reduce the number of groups I am in to make it easier to find the once that are active

can any one tell me how I can do this please
thank you