@Abdulaziz1391
Hi!
Did you mean to control the router on the Tether APP?
Since TL-WN840N only supports local management via Tether APP, so you might need to connect to the Wi-Fi of the TL-WR840N all the time to control it on the App.
While if you mean management via web UI, please refer to this link: https://www.tp-link.com/support/faq/1906/
Thanks a lot.