There are many ways to resolve the wavlink ac600 setup issues to resolve the extender issue following the lower steps.

Enhancing the Wavlink extender firmware: To improve the extender software, you will need to visit the Wavlink extender web management page with the help of the default web portal wifi.wavlink.com. After that, look for an administration option and then click on the firmware upgrade option. Further, download the firmware file, you will need to restart your extender device to finish this process.

Factory Reset Wavlink Extender: At the bottom of the Wavlink AC600 extender you see the reset hole button, push that button with the help of a paperclip for 8 to 10 seconds. Now, all the LEDs of the Wavlink AC600 extender will turn off. As it means, your Wavlink extender device is now completely reset.

Note: After the reset method, do the login and configuration process of the Wavlink AC600 extender.