I couldn't get it to see my Band 2, it seemed to be still focused on my Band 1. I contacted the Fanband team, here were their recommendations. It worked for me, I can now change my themes.
1. Uninstall fanband
2. Delete/remove your Band pairing via Bluetooth
3. RESTART YOUR PHONE
4. Re-pair you Band paring in Bluetooth
5. Do a full sync via Microsoft Health app
6. Reinstall fanband