I think you're talking about The Roku Channel, an app that Roku makes. If your TV doesn't have it, it doesn't have it. It appears that you are saying that a repair was done on your TV, and after a replacement motherboard was installed, your TV doesn't have The Roku Channel on it, and it's not available from whatever app store LG uses.
However, you also mentioned a Roku Premiere. That's a Roku streaming device that can be added to TVs to allow them to stream. I'm not clear why you mentioned it.
If you have a Roku Premiere, I suggest using it rather than the LG interface. It has The Roku Channel, of course, and access to thousands of other apps.
Roku Community Streaming Expert
Note: I am not a Roku employee.
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