@Yefrifer
Hello, after you configure the extender, it might have the same SSID as your router, thus the default TP-Link xxxx WiFi will not exist. However after a factory reset, the TP-Link xxxx WiFi should be available, so please try to reset the extender again by holding reset button/hole until all LEDs turn on momentarily.
You could also try different wireless clients, if none of them could find the extender WiFi after factory reset, I am afraid it is defective, please contact the retailer to check warranty.
By the way, if you connect a computer to the extender via Ethernet cable, are you able to configure it successfully and then use its WiFi?