Hi! This is really easy, as for it's the only way for me to edit my gauges. This is how I do it. I have VMWare with my bootcamp open in fullscreen where I edit my gauge. I save it, and drag it to the desktop of my mac. I open iTunes with my phone plugged in. Click on your phone, then go to apps, and then towards the bottom there is file sharing. Then click on DashCmd. It'll be there jailbroken or not. There's only one folder in there, and that's where all your gauges are. Drag it to your desktop, put your gauge in (if you just fixed a small thing, then you'll be replacing the old gauge) and drag it back in! The update is immediate, no need to restart the app, just select a different gauge, and then your gauge again.
Hope that helped! It's pretty straight forward