How do i fix this?

Null's Brawl
1

Ive seen alot of people download Nulls Brawl using the button from the install page on IOS. now when i installed it, it says:
Unable to Install
“Null’s Brawl
Telegram: @nulls_ios”

This app cannot be installed because its integrity could not be verified.

2

There’s an tutorial which I have sent to other people, I think you can find it.