Lionel 72 model O track Please help

Please help! My husband received a Lionel train set. We are thinking it is a 72 model. There are no numbers on the train other than the 8042 which is clearly the train number. We found it boxed and stored. We want to get it ready for Christmas for our grandchildren to enjoy. It runs in reverse motion. When we move the switch one way or the other it doesn't matter. It will go forward a couple of inches and then change to reverse again. What can we do to fix it.