Hi, you can simply flip the sprite to animate it to the left direction.
In the Inspector -> Flip H
If you use an AnimationPlayer Node, you can also key the flip h value to only be turned on, when animating to the left or do it via code in your movement script.
Something like:
if current_direction == "left":
$Sprite.flip_h = true
$AnimationPlayer.play("Walk")
Here is a tutorial by DevWorm where he does it with an AnimatedSprite: https://www.youtube.com/watch?v=pBoXqW4RykE
The flip happens at 15:50
I hope this helps, and you make a great game with it :)