Hi,
Thanks for visiting Apple Support Communities.
I understand that your iPhone will restart when using a third party application. I would start with forcing all open applications to close and restart your iPhone.
Close the app and open it again.
Turn your device off and back on.
- Make sure that you're using latest version of iOS.
- Open the App Store and tap Updates.
- If updates are available, tap Update All.
- If asked, enter your Apple ID password.
You might need a Wi-Fi connection to update some apps.
If an app you installed unexpectedly quits, stops responding, or won’t open
If the issue persists, I would recommend restoring the device. Make sure to backup your device prior to processing these steps.
Use iTunes to restore your iPhone, iPad, or iPod to factory settings
How to back up your devices using iCloud or iTunes
If the troubleshooting information that I provided still don't resolve the issue, see the article below.
If your iOS device restarts or displays the Apple logo unexpectedly
Cheers