2010 rancher 420 es
Hear a slight click but won’t go into reverse
Works ok in the other gears

 

When was the last time reverse worked? Have you been offroad in heavy sticks n Brush?

 

There is a lever under the rear of the engine which prevents engagement of reverse. This is operated by the thin cable on the LH handbrake lever, when you press the red button and pull the lever back. The cable could be stretched or broken, or the lever come loose. Over-adjusting the handbrake cable can also mean that the lever can't be pulled far enough back to disengage this reverse lockout lever. On most ES Hondas, there is also a switch on the lockout mechanism inside the engine, that prevents the shift motor from trying to get reverse, unless this lever is moved far enough, not sure if the 420 has this.