To use the 2.xx firmware, you will need to run ASIAIR app version 1.2. App version 1.2 will update the firmware to v2.61, if the ASIAIR hardware is not already using v2.61.
From my record of the firmware updates I have been archiving, the firmware vs released app versions seems to be
Firmware 2.61 ASIAIR app v1.2
Firmware 3.37 ASIAIR app v1.3
Firmware 4.55 ASIAIR app v1.4 (so far)
If you are on Android, you can look in your download area for APK files of the old apps (or find a friend who you can copy from). If you find them, uninstall the current v1.4 app, and install from the APK file.
If you are on iOS, there is no way to go back, unfortunately. I had at one time suggested to ZWO that they maintain a second iOS App whose content consists of the previous version of the app.
Clear skies,
Chen