During setup or when browsing to adjust settings, your Roku device will detect the HDMI connection to determine the supported frame rate and resolution that your TV supports.
When Auto detect is selected, your Roku device will automatically choose the highest frame rate and resolution. To leave your device in this mode, choose OK, go to automatic… after the connection check is completed.
Next, confirm the selected option if it appears correctly:
In Auto detect mode, your Roku device will set the display type to the highest supported resolution for your TV.