Trying to add an Airport Express to existing Airport Extreme network to extend WiFi range.

Power off the AirPort Extreme

Power off the AirPort Express if it is on

Power off the iPad Pro

Power up the AirPort Extreme

Power up the iPad Pro

Power up the AirPort Express and perform a Hard Reset on the device, then locate it near the AirPort Extreme

On the iPad.......

Tap on Settings on the Home Screen

Tap on WiFi

Look for a listing of Set Up New AirPort Base Station

Tap on AirPort Express

Follow the prompts

If the setup is successful, post back to check the firmware version. If you have not yet downloaded AirPort Utility, you can do so from the Apple Store. It's free.

Once the Express is up and running, locate the Express about half way between the AirPort Extreme and the area where you need more WiFi coverage.

Kind of a Catch 22 here. You can't check the firmware on the AirPort Express unless it has been configured and set up correctly, so let's work on getting the Express set up first. If there any firmware updates available, you can apply them once the product is up and running. Of course this assumes that the product is not defective......a very real possibility with a "used" or "refurbished" product.

It appears that you are using a Mac to try set up the Express. Is that correct? We can try a few more things using the Mac.

For now, power off the AirPort Extreme

Power off the AirPort Express

Restart your Mac

Power up the AirPort Extreme

Perform another Factory Default Reset or Hard Reset and then try the setup again.

Most users find it much easier to perform a Hard Reset than a Factory Default Reset, and they really are one in the same with an Express that has not yet been set up. So, try the Hard Reset as follows:

Power up the Express and let it run for a minute

Hold in the reset button for 7-8 seconds, then release the button

Allow a minute for the Express to restart to a slow blinking amber light status

If the setup is still not successful, is it possible that you might have an iPhone or iPad handy to try the setup with that device? If yes, post back for a few tips on this, since the procedure with the iPhone or iPad is different.

You don't always need to shut down the network, but it is always a good idea to do this as a troubleshooting step when you are having difficulty. It won't hurt if you want to try to set up the AirPort Express without powering off and restarting the other devices.....if you want to experiment.

Try to at least power off and restart the iPad, since you will be using it for the setup.

Nice work! Glad that you got things going.