Is this 2D or 3D? It's similar either way. Basically you have the enemy always move to their left (or right) relative to their rotation. In 3D, the direction can be found using the Basis, which gives access to the node's orientation. In 2D, you could do something like this:
var left = Vector2.LEFT.rotated(rotation)
rotation += rotation_speed * delta
move_and_slide(left * move_speed)
