Thanks for the clarification. Please follow these steps carefully.
Power off the Time Capsule by pulling the power cord from the back of device
Wait a few seconds
Plug the power cord back into the Time Capsule
Restart your Mac
Temporarily, locate the AirPort Express in the same room or close proximity to the Time Capsule
Power up the AirPort Express....if it is not already on
Hold in the reset button on the back of the AirPort Express for 5 to 6 seconds, then release
Allow a full minute for the Express to restart to a slow, blinking amber light status
The AirPort Express will NOT appear in AirPort Utility until it has been set up. You have to run the setup "wizard" on the Express...and then....it will appear in AirPort Utility. This is likely where you are having the problems.
Click the WiFi icon at the top of the Mac's screen
Look for a listing of New AirPort Base Station
Click directly on AirPort Express just below that
When you click on AirPort Express, that will get the setup "wizard" running. It will take a few seconds to analyze the network and then display a screen that looks similar to this......except that you will see your devices pictured with the name of your network.
Type in a simple, short name that you want to call the AirPort Express
Click Next
The setup wizard will configure everything for you automatically
When you see the message of Setup Complete, click Done
Now move the AirPort Express to a location that is about half way between the Time Capsule and the general area where you need more wireless signal coverage. The more that you have line-of-sight between the Time Capsule and AirPort Express, the better the network will operate.