As long as you are the admin on the account, you can add users by going into “my account” on your dashboard.
From there, “user maintenance” and on the next page, scroll down and press “add user”.
Please ensure the email address is the one they intend to use and the customer account (your business) is exactly the same.
After creating this account you can reset the password to give them their own access by following the same steps above, but on the user maintenance screen, scrolling until you see the new user and pressing “reset password”.