@amany
If you look in the WC Vendors core files, the sold by is determined in several locations.
wp-content/plugins/wcvendors/classes/front/class-vendor-shop.php
wp-content/plugins/wcvendors/classes/front/class-vendor-cart.php
For each instance you find the sold by being defined– you’d have to write a filter to change it. $sold_by
Instead, There is also the template, which can be modified:
wp=content/plugins/wcvendors/templates/front/vendor-sold-by.php
And you could write your own function to call the userpro profile link in that template instead of the $sold_by
How to modify templates: (https://www.wcvendors.com/kb/changing-vendor-templates/)