Hard reset TP-LINK TL-WDR4900

Factory reset (Hard reset) The reset button is located on the rear panel and it’s labeled WPS/RESET. You need to press and hold it down for approximately 8 seconds while the router is powered ON. You should release the button when the SYS LED becomes quick-flash from slow-flash. Then wait for a minute for the router to restore its defaults.
Firmware Firmware link
Default username admin
Default password admin
Default IP address