@bahage, before you make any changes, go to the Paramount+ website and enter the email address that's displayed on your Roku device under Settings->System->About and then click the "forgot password" link. Hopefully you'll get an email allowing you to reset/create a password. If that works, you can use the email address and password to log in on any device.
I have no idea what a subscription directly with Parmaount would cost, but they probably have different options than what's available through Roku. If you cancel your subscription through Roku you'll still have access through the end of the current period, so if you also start a subscription directly with Paramount you'll now have two active subscriptions. That's what period overlap means.
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