How do you reverse polarity on left tire

I'm thinking you mean the whole chair goes in circles right? If so, and it's spinning to the left then you have a problem with the left motor. First thing to do is remove and inspect the motor brushes. There are two of them on each motor and you can find them by locating the small black plastic circles with slots in them. Take a flat screwdriver and unthread the plastic disk. Then use the end of the flathead to pop the brushes out. The spring should be silver and pliable. The black head piece should be clean without a lot of debris and the wire should be a shiny copper. If they are dirty, clean them with a q-tip, also clean out the hole into the motor where you took them out. Reinstall and see if the chair will run. If not, replace the brushes and retest.