Go to showtime.com/optimum and enter the email address for your SHOWTIME account. Once you sign in, you will be prompted to enter your Primary Optimum ID and password. Once completed, this will link your SHOWTIME account to your Optimum account.
Alternatively, you can sign into your SHOWTIME account and navigate to Account Settings, which can be found on the upper right corner of showtime.com. Select ‘Your Subscription’ and click ‘Link Your Internet Provider Subscription.’ You will then be prompted to enter your Primary Optimum ID and password.