Certified GKH Gardening Expert
If they are hardy hibiscus, you do not need to do anything. They tolerate winter very well without help.
If they are tropical hibiscus, they will not be able to survive in the ground over the winter. You will need to dig them up, place them in pots and bring them indoors for the winter.
This article has some thoughts on the subject: https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/wintering-hibiscus-indoors-winter-care-for-hibiscus.htm
If you want to try pulling them through the winter, you can try some of the strategies outlined here for fig trees: https://www.gardeningknowhow.com/edible/fruits/figs/fig-cold-protection.htm
Of course, it occurs to me that you may be talking about Hardy Hibiscus. In which case, your plants should have no problem making it through the winter.