1995 Chevy Blazer gear problem

please help!  we have a 1995 chevy blazer suv and the parking gear won’t engage .  It registers as reverse when it is in park, and won’t start unless its in neutral. we were able to move something under the vehicle to make it engage, but as soon as we put it in drive, it goes back to before. how can we adjust it ourselves, and where do we look?

TSB 01-07-30-021 Park/Neutral Position Switch Connector cannot be Removed (Replace Switch and Connectors)