I have an app Hicalculator, since de new version of iOS update this app stop working, showing a message that "Needs to be updated" the developer of this app didn't updated this app for the new iOS version

AppUpdated wrote:

How to contact a developer of the apps

Don't waster your time. For one thing, there are multiple "HiCalculator" apps in the store right now. Clearly, the one you have is not on the store any longer. There is no way to tell if it is at all related to the current ones. Your receipt from Apple should have the name of the developer listed. But even with that, the developer has clearly abandoned the app.

On macOS, the application requires Big Sur (macOS 11.0 or later) and a Mac with an M1 chip. On iOS, it requires iOS 8.0 or later. There is no link to the developer on iOS/iPadOS, but on macOS, the developer's link is present in the Mac App Store page for this application. Don't get your hopes up.