To open my app

Can you elaborate? We may need a bit more information to understand the issue.

Writing an effective Apple Support Communities question - Apple Community

1. Which app did you want opened? What happens when you try? Do you get an error message? What does it say?
2. You posted in the QuickTime forum. QuickTime Player as an app is not available on iPhone (not needed as player: modern MP4 and MOV files can be played just fine).
3. Did you perhaps mean QuickTime on a computer? If so, what model computer with what version system software?