My guess is you'll have to cancel the subscription that you had through the Roku channel because those are only good within the Roku channel on a Roku, not the freestanding channel. (At least that's how AMC+ subscription via the Roku channel worked for me.)
Then add the Paramount+ app on the Samsung smart and re-subscribe. If you have Paramount+ Essentials through Walmart+, though, I think you can just enter your login info in the Samsung Paramount+ app and go from there. Assuming, of course, that there is a Paramount+ app on Samsung.
The other thing you could do is buy a Roku Express or 4K Express+ or a Stick, plug that into the Samsung, switch the input to the Roku, and watch all your Roku stuff that way. Your Roku account and that subscription through the Roku channel would transfer over since it is good on any Roku device.
I don't know what apps are available on modern Samsungs. My only Samsung is old, like 2016 or so old, and I have a Roku Stick on it. Sometimes I watch the Samsung offerings, sometimes the Roku Stick, but it's a tv that gets only occasional use so I put my spare 3600x Stick on it.
