I bought this streaming device 50days ago (according the device) I noticed it doesn't have prime video on it. I've tried using the roku website to add channel unfortunately it's not highlighted.
That usually indicates a location issue. What country are you in?
It may not be available on the device in the location you currently live.
Country of residence is UAE how do I fix this?
UAE, is there a way to fix this or change country to access prime video
Roku tends to restrict those things as well as the apps tend to block or restrict efforts to do so.
Amazon would need to mark their Roku app as being available throughout the world (not just countries that Roku itself supports.) You can encourage them to do so. Some streaming services have actually been surprised that they had limited their apps in that way, but others do it intentionally.