I'm having a slight issue with my 4-wheeler. It goes Forward or Reverse and Left or Right but if I want to turn L/R while moving F/R, it will not do it. Any help will do, Thanks

PARTS: 1 - EZ-B 2 - 2.5A Motor controllers - One's in EZ-Robot store 2 - Standard DC motors for Forward and Reverse 1 - Standard DC motor for Left and Right