@Traveler2020
Log into your router and see if there is an option in the wireless settings to switch the wireless security to Auto or WPA/WPA2-PSK and the encryption to TKIP/AES.
You can also set specific channels for each wireless band in the router then reboot the extender.
If you still get no internet, disable the wireless security on your router, then factory default the extender and connect it again. If it does connect test the internet to see if it works. If it does, re-enable the wireless security on your router, use the Tether app to connect to the extender and connect it back to the router.