The Roku app you are probably referring to is The Roku Channel. It is available on Samsung sets, along with some other devices. It does not give access to channels available on a Roku player. It only provides whatever content is available within The Roku Channel itself.
There's no need to remove the Roku app from the TV to use a Roku Stick, or any other Roku player. Simply connect the Roku player to an available HDMI port on the TV and use the TV remote to change to that input. If it's a 4K TV, make sure you enable UHD Color for that HDMI port in the TV's settings, to ensure you get full 4K/HDR.
But if you want to remove the Roku app from the TV, I believe you simply long press the button on the remote to get an options menu and select remove/delete from that menu.
Dan
Roku Community Streaming Expert
Help others find this answer and click "Accept as Solution."
If you appreciate my answer, maybe give me a Kudo.
I am not a Roku employee, just another user.