Apple’s Calculator

Good Afternoon everybody,

I need help with a friend’s device. After all she owns an iPhone XR. Since a couple of days, we can’t find the Calculator Icon in her desktop. We have already checked all the pages and files but it’s impossible to find it! So we have tried to download it again. Unfortunately we can’t because into App Store we can only press “open”... it seems the calculator is already set up into my friend’s device but it’s hidden somewhere!

How can I make the calculator icon appear again in the desktop?

Thanks in advance anyone who will answer.

Francesca