You can check the position of the player, and add an offset to the y-value,
Add this to your enemy-script:
export var offset : float = -800
func _process(delta: float) -> void:
var Player : KinematicBody2D = get_parent().get_node(("Player"))
position.y = Player.position.y + offset
You should probably save a reference to the player-node in _ready and use that instead, so you dont have to check every _process-call.
I hope i could help you with that.