In the Slider Editor you can arrange the layers. It has a point when the layers are above each other. So the layer which has larger number in the beginning of the layer strip, which means its position, then that will be above each other.
How to arrange the layers?
So when you are in the Slider Editor, scroll down to the layers. You can see a three-line icon, like a burger icon on the left corner of each layers' strip. You can grab the layers with this icon, and simply put it to the desired position by a drag 'n' drop.