This video, which accompanies the January 2023 Horse Deals article, will help you understand the process of teaching your horse to long-rein.
One safety point that I would like to make - I suggest that you do NOT allow the reins to drag on the ground as I do in the video. I have been long-reining for many years and am always aware of where my reins are, however, when you first begin, I recommend holding the reins in your hands but be sure not to wrap them around your hands.