The best method is to add users to the box application via a group membership. That way you can assign the role user type to the group. For example here's my Box application configuration page for group assignment:
Then select the pencil, and assign box group and user role assignment profiles that you want.
Once done you can just add the user to the group and they will get added to box with the detail already assigned. The group can be a regular Okta group, AD or any other application group assigned to your Okta tenant.