Find my iPhone

Hi there

See this on how to turn find my back on

1. Open the Settings app.
2. Tap your name, then tap Find My.
3. If you want friends and family to know where you are, turn on Share My Location.
4. Tap Find My [device], then turn on Find My [device].
5. To see your device even when it's offline, turn on Find My network.* 
6. To have the location of your device sent to Apple when the battery is low, turn on Send Last Location.

On the phone go to Settings > [username] > Find My and turn it on.

Also see: Set up Find My on your iPhone, iPad, iPod touch, or Mac - Apple Support