[Q] Beginner, looking for help; modding Striiv fusion topic

I have been studying programming and the like recently, and I wanted to work on something practical. I recently got a 'Striiv Fusion' and wanted to learn how I can edit the firmware inside the device, to make a few simple changes such as the order in which screens appear.

If anyone could help; I want to know how I can get access to the code in some form for both the Wrist-Device and the Mobile app. Then how to redeploy my edited version of the code into the device/phone.

In addition:
I'm very unfamiliar with this sort of thing, and would appreciate being directed towards any references I could read up on.