In this case, you need to follow below-mentioned steps-
first of all if you made any changes on it you need to reset your Belkin Range Extender by pressing the Reset button for 20 seconds(while it's powered on).
Once the Extender lights stop flashing then you can easily reconfigure it simply by performing WPS Method on it.
To do WPS process you need to press the WPS button of your home router for 3 seconds and then within 1 minute, you need to press the same WPS button of your Belkin Extender for 3 seconds.
Once you find that the lights of the extender are solid/stable, you can connect to its network using the router's WiFi password with any of your wireless devices and then try to go online so that you come to know its working fine.