Restore Factory Firmware for TP-Link RE450


I've a repeater which I wanted to try with OpenWRT, but the UI/Software is very unconvinient and doesn't work as repeater for 2.4/5GHz or I'm too dump.

I've tried the method to restore to factory firmware with TFTP server, but it won't collect the file and won't connect to the server either. So what's the matter and how can I fix it?

Thank you guys.