Just bend a thin branch from near the bottom of the plant down and bend it down to touch the ground. Cover it with mulch. Place a brick on it to hold it to the ground. Keep it watered. Roots will grow from where this branch into the ground. When the roots are grown, cut the original branch from the first bush and plant the new growth in the ground or in a pot if you prefer.
You cut a piece that has no flowerhead. Cut about an inch below a pair of leaves. Re-cut to just under the 2 leaves and Strip of the leaves and dip into water and then Root powder. Pot up at edge of pot, that way you can take a few cuttings at the same time water and wait for new leaves or signs of growth. Pot on next year when hopefully you should have a good lot of roots. Best of luck............