Welcome, mussa145!
From your post, it sounds like you are trying to open a 3rd-party app that is installed on your iPhone. We’re glad that you reached out to the Apple Support Communities. We want to try and help you find the answers you need. What type of iPhone do you use? What version of the iOS software do you currently have installed on your device? You can find this in Settings > General > About.
Have you ever been able to open this FileGet app without an issue in the past? If so, when was the last time you were able to open it successfully? Also, have you tried to remove the app and reinstall it to your device? If not, try that to see if it corrects the issue.
Also, please Restart your iPhone. Does this help to resolve the issue? Often this simple step will refresh the apps and software on the device to solve numerous problems you may encounter.
We hope this information helps you out.
Take care!