Hello,
If you do not want to allow the people that they can register by themselves. You can disable the registration on your site from WooCommerce >> Settings >> Accounts & privacy >> Account creation.
Screenshot for clarification: https://jmp.sh/Esqzhj9
You can mention in your contact us page. That the persons who wants registration on your site have to contact you by contact us form.
So when you get a request from customer side. You can create a new user from “Users” option and assign a “customer” role and then share the login info to that specific customer.
Screenshot: https://jmp.sh/l3ji1wF
Best Regards.