Roles and User editing

I have a woo-commerce site that has Customers, Store Vendors and Store Managers.

Store vendors are able to use a particular page on the website to submit a product as draft to be reviewed and published by the Store manager.

We are getting a few customers who want to change from a customer to a vendor so that they can submit products.

The Store manager is not presented with this option when editing a user, in fact they are not given any option other than “non for this site” or “Customer”

What permissions do I need to change to give the Store manage the ability to “promote” a customer to a Store Vendor.

I do not wish to make the Store Manager a full administrator as they may give someone the wrong role and cause major issues on the site.

I would just like to give the “store manage” the option to change a user from Customer to Vendor.

Any suggestions appreciated!

Thanks