Watching my channels on laptop

mahziar 

For most subscriptions "through Roku", you are limited to watching them on the Roku device or through the Roku Channel.

Try going to the online Roku Channel, login, and see if you can access your Paramount+ from there.  https://therokuchannel.roku.com/

Otherwise, may be able to access it through the official Roku Mobile app (mobile devices/tablets). 

https://www.roku.com/mobile-app

https://support.roku.com/article/217288467

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If neither of the above methods work for you, then you might want to consider signing up with Paramount+ directly which will allow to watch on both Roku and non-Roku devices.  https://www.paramountplus.com/