Is to move the extendee(?) closer to the connection you want to use.
I am using a WiFi range extender Netgear model no WN 300GRP I am not able to find a particular WiFi signal which I find in my mobile and laptop in the list of extender mode of the router what is the cause but I can see other signal which is of no use

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic