There are a few possible causes if your Walker zero-turn lawn mower will only turn one way. The first thing to check are the linkages, if they are broken or missing then you would need to replace them. If the linkages are all good, then you may have a bad hydraulic pump or wheel motor which would need to be replaced.
The model and serial numbers on your Walker zero-turn mower can be found on the frame of the mower.
NOTE: if you need a part for the small engine in your Walker zero-turn mower, there will be a separate model/serial number for the engine. Here are the small engines that are available in your Walker mower. Visit the page of the engine you have to find out where the model/serial number is located for your small engine model: