Creating a new Salesforce User with System Administrator access is straight forward.
In the Red box, you’ll notice this user has been assigned User License: Salesforce. If “Salesforce” is not an option, you will need to go and disable another user.
Make sure you also select “System Administrator” for the Profile.
You can actually make the Username whatever you want; even an email that does not exist. We usually prefer customer@junorocket.com (replacing ‘customer’ with your company name.
The email address does need to exist, so please confirm that we have actually setup the customer email address. If we request this account, it typically means we’ve created that address.