If your plant is big enough it can be divided. If it has produced seed - worth sowing in spring. Or taking stem cuttings 4-6" and put into damp sharp sand or vermiculite/perlite and keep warm, and somewhat humid until they form roots. Put your pot with the cuttings into a plastic baggie that you can fasten and open to allow fresh air. If you have a warm glasshouse area it should be easy. Just allow good light without direct sun otherwise the cuttings burn/wilt.

Cuphea hyssopifolia - short-lived but does self-seed. Has pest potential in warm areas but reliable winter frost should see it kept to civility...

Winter frosts should do the trick :-) It is unlikely to survive them! This is a semitropical plant that is typically sold as an annual in zones colder than 9. Will not overwinter in my zone 8.