Hard reset TP-LINK AC1900 / Archer C9

Factory reset (Hard reset) Turn on your router and locate the WPS/Reset button on the back panel. Press and hold this button for more than 5 seconds to reset the router to its factory default settings. Visit http://tplinkwifi.net to create a new login password.
Firmware Firmware link
Default username N/A
Default password You set it at http://tplinkwifi.net
Default IP address