Once the customer registers on your Magento store, the customer will see Marketplace option in My Account section. The customer will go to Marketplace>Become Partner, tick the checkbox (Do you want to become seller/vendor?) and enter a Shop URL.
An email will be sent to admin/store owner. Once the admin approves the customer’s request to become a seller. That customer will get an email notification.
For further queries or customization, please send an email to [email protected]