Someone left a comment about a 3 Day Diet App so I went looking.
I haven't had the chance to install any yet but some have really good ratings.
So if your looking for an app to help you follow the 3 Day Diet plan here are some options:
App Name Creator Android/Apple Cost
3 Day Easy Diet app APP2SHOP Android Free
3 Day Diet Realized Mobile Android $1.99
3 Day Diet Realized Mobile Apple $2.99
3 Day Diet and 1200
& 1500 Calories Diets Post799 Apple $0.99
Just click on the name and it will take you right to the app where you can install it. The one with the best rating would be by Realized Mobile on Android. There is no rating for the one on Apple but it is by the same company.