When you want to share the screen on a Roku TV, the first thing is to ensure that your TV and phone/PC are connected to the same Wi, Fi network. After that, on the Roku TV, navigate to Settings > System > Screen mirroring and choose either Prompt or Always allow. Hence, on Android, turn on Cast/Smart View and pick your Roku TV; on Windows, hit Win + K and select the Roku device. iPhones, however, will have to install a third-party AirPlay app as Roku does not have native AirPlay support for all models.