There are many species of hibiscus. The overall majority are best propagated through cuttings. However, hardy hibiscus can be divided and is usually done so in spring. It can be divided by cutting the plant in half. Stick a shovel in the middle of the plant between the stalks and cut straight down into the root ball. Then dig out from around the plant (about a foot around). Pop them up out of the ground and then replant.

Here is an article you may find helpful: https://www.gardeningknowhow.com/garden-how-to/propagation/propgen/dividing-plants.htm