Unsucessfully trying to set up wireless access point with Airport Express

In order to set up the AirPort Express as a wireless access point, it is a requirement that an Ethernet cable connects permanently from one of the LAN <--> ports on the main router to the WAN (circle of dots) port on the AirPort Express.

It is not possible for a single AirPort Express to connect to an existing network using a wireless connection and service as a wireless access point......unless.....the AirPort Express is connecting to wireless network that is being provided by another Apple wireless router.

It is possible.....but also extremely unlikely.....that the main router there is an Apple product, but you might check on that possibility.

Another option.....somewhat complicated.....is that it might be possible to use two AirPort Express devices to connect to the network. The first AirPort Express would be configured to "join" the wireless network. Then, an Ethernet cable would connect from the first Express to a second AirPort Express which is configured to create a wireless network signal.

Most users will need the help of another person who "knows computers and networking" to set up something like this.

Something like a Netgear WN 3000RP might be able to do what you want.

Unfortunately, the only way to know IF it will work is to try it out in your home, so you would want to make sure that you understand the store's return policy before you buy......in case things do not work as hoped.