To allow users to edit their profiles, you need to create a menu item for “Edit User Profile”
Create a new menu item in a menu that you want, select Users -> Edit User Profile as the menu item type.
Access the new menu item in front-end, login with a merchant account, you can see the form to edit profile which includes merchant’s profile fields.
As an administrator, you can always edit any user’s profile in User Manager.
Administrator can add and edit meta description and meta keywords for merchant, merchant can’t do this by himself in front-end. Meta description and meta keywords are used in merchant’s detail page for SEO purpose.