"Join" problems are almost always a result of non-matching settings for wireless security between the "main" router and the "joining" AirPort Express.
The Expess must be provided with 3 correct settings in order to "join" a wireless network
1) Wireless network name
2) Wireless network password
3) Exact same wireless security setting that the "main" router is using.
Most users know 1) and 2), but do not know, or guess at 3). Unless all elements match up correctly, the Express will never "join" the network.
The key question here is likely......do you know the exact type or wireless security that the Technicolor router is using?
This is what I see the router is set up with - can the A1088 Express work with those settings or do I need to change something in the router? Rather not change the security settings on the router of possible as we are 3 people using it and probably 15 devices using the router...
Security Mode: WPA-PSK
WPA-PSK Encryption: TKIP&AES
WPA-PSK Version: WPA&WPA2