Struggling to setup airport express wirelessly to extend wifi network

Unfortunately, you received incorrect information from what may have been an overly optimistic sales person, who apparently did not even review the capabilities of the Express in the Apple product information.

The AirPort Express can only wirelessly extend the signal from another Apple router.....an AirPort Extreme, AirPort Time Capsule, or another AirPort Express.

Take it back and swap it for an extreme?

No, Apple uses proprietary settings for their extend feature....which the sales person should have known if he was paying attention during training....and those proprietary settings are designed to only allow other Apple products to work with each other to extend a network wirelessly.

Another way of saying the same thing is that in order to extend an Apple network wirelessly......you need two Apple routers.

IF.....you want to run the long Ethernet cable from the Express all the way back to your main router.....and leave it connected at all times.....then the Express can be configured to do what you want that way.

My advice would be to return the AirPort Express for a refund and try another product from another manufacturer....like Netgear or TP-Link, for example..... that will be compatible with the main router that you already have.

If you want to buy another AirPort Express to be installed near your main router.....then we can make the other Express wirelessly extend the signal from the first.