I have a wcmp and woocommerce based multivendor website with a lot of products and vendors added already.

Hi, @dantefour

If you don't want to lose all your data, so please do not click import data. If not, all data of the demo will replace yours.
So if you want to have any pages of the demo, please refer to this document to understand: https://ecotech.kute-themes.net/documentation/docs/faqs/5-how-to-import-the-specific-pages/

If you cannot do it, please provide me your admin account and let me know what you want to do, I will check then help you

Regards,
Yame