Note: The PodExpress has plastic-standoffs, with thread-cutting screws. The process outlined below should be done with a hand-screwdriver, and NOT a power-drill/cordless-screwdriver of any sort. Take your time, and as your tightening it's better to tighten a little, check for wiggle, and repeat, than over-tighten.

Set your PodExpress face down, and remove the 4 screws on the bottom (mine are already removed in this photo):

Tilt the plate, and plugin the Aux plate as seen below:

Then simply lay the plate down onto the back of your PodExpress, and use the included longer-screws to install the plate to your PodExpress

Congratulations, it's installed! Now for one final piece: configuration

Hit up your PodExpress manual (here's a link to Line6's site: https://line6.com/data/6/0a020a40152f865e216d6d6b24/application/pdf/POD%20Express%20Owner's%20Manual%20-%20English%20.pdf)

Head to page 27/28, and you'll want to get into your Global Settings and change option #3: Volume Jack. By default, it comes setup for a Volume Pedal + 1 footswitch. You'll need to change it to 2 footswitches (FS3/FS4)