@Mocharla-65. Hello,
You could factory reset extender and install it from scratch:
RESET: With the extender powered on, use a pin to press the RESET button until most Leds flash once.
Later please follow the instrucions here to set up range extender :
(How to configure Range Extender via Tether APP)https://www.tp-link.com/support/faq/357/
(How to configure my range extender via web GUI to extend an existing wireless network's coverage)https://www.tp-link.com/support/faq/1400/