@Tommac 

You want the extender to be in the same room as the router when you initially configure the device. Once the setup is complete it is saved so you can move the extender after.

Plug in the extender and look at the LED light to determine the status of the device. You mentioned four bars so if the power light was light, Wi-Fi, and at least three or more signal lights on, then the device is already configured. 

If you look at your wireless network, and you still only see your original Wi-Fi name, then the extender is using the same name of your router so only one name appears. 

It would be best to make sure the extender has a different network name by using the Tether app. Since you already have it downloaded, connect your phone to your router, then open the Tether app. The extender should find the device and list it.

If you plug in the extender into the same room of the router and only the Wi-Fi and power light are on, factory reset the device by holding the reset pinhole below the device for 15 seconds. After the extender reboots, it will begin broadcasting the default TP-Link wireless network. Use the Tether app to then configure the device: https://www.tp-link.com/us/support/faq/1373/

The extender uses the same wireless password any of your wireless devices would use to connect to your Wi-Fi so it would be best to verify the password being given to the extender is correct. To do that, forget the wireless network of your router, and connect back to it. It will prompt you for the wireless password, enter the password to verify you have the correct one so when you reach Step 4 in the Tether setup that is where the password would be entered.