So I believe what's wrong is that the KinematicBody2D was either inside of another collision object OR you didn't hook up the movement script the right way. If it is inside of a collider, Just move it out. This is how I would go about moving the character.
self.position.x += 5
self.position.x -= 5
This is a very simplistic version of movement to left and right. I hope this helps :)