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.
func _process(delta):
if Input.is_action_pressed("Move_Right"):
self.position.x += 5
elif Input.is_action_pressed("Move_Left"):
self.position.x -= 5
This is a very simplistic version of movement to left and right. I hope this helps :)