Be sure to replace the plastic casing removed in steps 2 and 3 in its original orientation.

There is a little shield molded into the plastic casing that should line up with the security slot at the far right of the back panel. The shield serves (I presume) to keep stuff from getting through the slot and into the inside of the AirPort where it could cause mischief. Also, if it is in the wrong place, one or more of the screws may not be possible to screw in and/or the casing will be distorted if you force the screw(s) in.

If the reset button does not work, the switch that it presses on may have been damaged or have come detached from the logic board.

If you remove the bottom pad and plastic bottom of the case, following instructions elsewhere on iFixit, you can either just remove the switch (if it is still attached!) and bridge the two pads that it connected or the required amount of time, using that paper clip bent to fit (or similar). The two pads nearest the edge of the board seem to be used only to mechanically attach the switch to the board; the two pads set back from the edge and originally soldered to the contacts on the back of the switch are the ones that need to be bridged to reset the unit.

Alternatively, you could remove the logic board and re-solder (and if necessary, replace) the surface-mount switch .

It’s easier just to bridge the pads , and if you remember the password you won’t shouldn’t ever need to use the reset button again.

On my well-aged unit, it was not necessary to apply heat, just to work slowly and carefully.

The pad came away cleanly and all of the old adhesive remained on the plastic body of the unit.

It was not necessary to use double-sided tape, as the pad re-adhered adequately without it and remained easy to remove.

By the time I needed to open my AirPort Extreme in mid-2019, the adhesive bond to the covering had weakened to the point that the covering readily peeled away cleanly without the application of heat. I just worked slowly and carefully.

The covering had no residue of adhesive on it after removal, but there was a sheet of adhesive clinging to the plastic surface of the body of the unit. I had to poke holes in it to reach the screws, but that was no big deal and easily done.

When finished, the rubbery covering adhered to the body of the unit again adequately without the use of additional adhesive or (as I had planned to use) double-sided tape.

BTW I was not disassembling the unit to replace the battery, but rather to reset the device by bridging the contacts that a broken reset switch failed to connect. (The switch had become detached from the circuit board and was literally hanging by a thread when I opened the case and fell off altogether as I examined it.)

Thanks for the clear disassembly instructions!