If you need to assign roles to a large number of users, you can upload a text (.csv) file to bulk assign roles.
Note: Member does not need to be assigned as this is the default role.
Step 1: Head over to "Site admin" > "User Management" > "Bulk upload users."
Step 2: Upload your populated (1) CSV file and then click on (2) "Bulk upload users via CSV."
Step 3: Review user information then click on "Bulk upload users via CSV."