Use a user's previously entered information to do calculations on current form

Use a user's previously entered information to do calculations on current form

Hi!

My premise is that a user will access the app, enter data in a form for example: amount of bananas: 1 banana.

Next day they go in and enter the same form, while other users also update their own form data, stating the banana amount for that day.

I would like to add logic so that if the bananas are a different amount from the previous day, it adds a question: "why are there less bananas today?" so that the user can say what happened to the banana.. So basically it's stock taking.

How can I retrieve a user's previously entered info in order to calculate logic in the same form? Do I need a separate form with usernames and ids?

Thanks,

Ale