Oh sorry, I was just using the code from the tutorial. With AnimationPlayer you would use seek. However seek takes a value in seconds, not frames. So you will have to calculate where exactly that frame is in the animation is seconds. Assuming all the animations have the same length, you can do this:
var current_position = $AnimationPlayer.current_animation_position
$AnimationPlayer.play("run")
$AnimationPlayer.seek(current_position)