This is a Web based app, explained in Guide 1...but it may be your browser. "Add the DDF app to your phone home screen

As part of the onboarding process, you will be guided to add the DDF app to the home screen on your phone. Once you do this it will look and feel like a native app.
To do this on iPhone open https://app.datadrivenfasting.com/ in Safari (not Chrome or Edge) and click on the square with the arrow at the bottom of the screen.
On Android, tap on the menu icon (three dots on the top right) and select add to home screen.
Voila! You will now see an app icon on the home screen of your phone.
You will be able to access DDF from your phone or your computer"

Just an aside...there are so many FB pages! One for DDF program in general, the one created for this challenge and other previous ones. A Nutrient Optimizing FB in general, one for the Masterclass. And if you want to look at meals optimized...ask to join FB group Healthy Low Carb & Keto Recipes. Then there are all the websites, Instagram etc