Allow the vendor to upload his own products

we've followed the articles that has been provided for the configuration, But I've 2 major questions

1. I've tried following the articles to allow the vendor to upload his own products, by changing his settings from the:
           a. Configuration > Settings > Vendor Settings
           b.  Configuration > Settings > Access Control Settings
I couldn't pass through  and the Vendor still couldn't upload his products / services
2. how could I allow the Customer for request to be a vendor.

Did you follow these instructions
https://docs.nopcommerce.com/en/running-your-store/vendor-management.html
Once setup you can login as the vendor and goto Admin to add products

Link to appy to be a vendor in the footer
https://yourwebsite.com/vendor/apply