@Leese Hello, 

As RE use the same wireless password as router, when RE use the same SSID as main router, Wi-Fi clients could roam to the stronger Wi-Fi by itself. 

If you want to 'see' RE as a different SSID (Wi name), you could change a different SSID for RE using Tether app, and manually connect your other devices to RE's SSID. 

(via Tether app)How to change wireless settings of TP-Link wireless router on Tether APP
https://www.tp-link.com/support/faq/2541/