@Florence-Hur
Hello,
Please check and make sure you have the correct wireless password from your main router, you may forget the wireless connection on your phone and try to connect back again to confirm if the wireless password is correct or not.
If the router password is correct, please reset the WA860RE first: With the extender powered on, use a pin to press the RESET button for 1 second until the LED turns off then on. If not, try to power off the main router, then power off the extender and power it back on and try again.
Please watch the setup video or follow the instruction to configure it.
Setup Videos
How to configure my Range Extender via Web GUI
Note:
Please use your home wifi password to configure the 860RE.
We suggest you customize the network name for the extender. You can see it in step 3.
May it help, and have a great day.