Try force quitting the app
Force close an app iPhone X
iPhone X
- From the Home screen, swipe up and pause.
- Firmly touch and hold the app, then tap
You can also swipe up to close the app as soon as you see
iPhone 8 or earlier
- Double-click the Home button to show your most recently used apps.
- Swipe right or left to find the app that you want to close.
- Swipe up on the app's preview to close the app.
Try restarting your iPhone or iPad
Restart your iPhone X
- Press and hold the Side button and either volume button until the slider appears.
- Drag the slider to turn your iPhone X completely off.*
- After your iPhone X turns off, press and hold the Side button again until you see the Apple logo.
Restart your iPhone 8 or older model, iPad, or iPod touch
- Press and hold the Top (or Side) button until the slider appears.
- Drag the slider to turn your device completely off.*
- After the device turns off, press and hold the Top (or Side) button again until you see the Apple logo.
Try deleting the app then reinstalling it
Delete an app
- Lightly touch and hold the app until it jiggles.
- Tap
in the upper-left corner of the app. - Tap Delete.
If you press too firmly on an app, you might open the app's Quick Actions menu you may open the Share menu if you press the app too firmly.
Check your iPhones battery usage
Go to Settings > Battery.
To see how long each app has been open and running in the background, tap 
Under each app, you might see these usage types:
- Background Activity means that your battery is used while apps run in the background.
- Audio means that apps play audio while running in the background.
- No Cell Coverage and Low Signal means that your device is searching for a signal or being used with a low signal.
- Backup & Restore indicates that your device has been backing up to iCloud or restoring from an iCloud backup.
- Location and Background Location means that your battery was used when tracking your device.
Adjust settings to improve battery life
Try enabling Auto-Brightness or Adjust Display Brightness to a lower setting.
Use Low Power Mode
Try extending your battery life by turning on Low Power Mode. You can enable it by going to Settings > Battery.
Low Power Mode reduces display brightness, optimizes device performance, and minimizes system animations but has no negative impact on the Nanit app's performance.