You can order the fob in the application by heading to the Card section, selecting the Devices sub-tab (top right) and then selecting Order MuchBetter Fob.
The fob costs 9.99 GBP (or the equivalent in another currency).
If you haven't verified your documents yet, you will be asked to do so now.
Once the verification is complete, return to the Devices tab and request the fob.
It generally takes about 5 business days (UK) or 10 business days (EU) to arrive.
Once you have received your fob, you need to activate it in the app. Just log in and go to Card -> Devices subtab. Then swipe left to the activation screen and enter the 9-digit code and the Nickname of your fob. Finally, tap on Activate.