Change gear on the App
I've had AXS for 7 months and while I was out last week the shifter battery went flat (I was expecting it to last a year). I was 10 miles from home and found a CR2032 battery in an emergency rear light I carry in my pack so got going again. If not for this I would have been stuck in the last gear I was in which may not be ideal for limping home. If it was possible to select a gear from the app then a compromise gear could be selected, and even changed now and again if really necessary.
There is also a bug in the AXS web notifications. In the run up to the shifter battery going flat I kept getting notifications that the derailleur battery was going flat, it wasn't, I'd only just charged it so I ignored them. The notification was probably about the shifter battery, just incorrectly labelled.
press the button on the shifter to shift down a gear. works for both front and rear derailers