Because this is a standing drill we want to start off in a nice neutral spine. To find this, imagine your pelvis is a bucket of water, tip it all the way forward, so the water is pouring out the front. Then, tip it all the way back, so the water is pouring out the back. Then, find the middle of those two end points. You will find this is a relatively neutral spine and probably requires some muscular effort to hold this.
Once you have found that neutral position you can do this with feet shoulder width apart or split stance like in the video. Then, slowly rotate away from the band. Make sure on the way back you are even slower, take about 3-5 seconds, this is where the magic happens.
This rotational drill has many variations which can be done throughout the whole pregnancy and very soon after the delivery.