Welcome to Apple Support Communities.
I understand you've disabled Find My iPhone, and you'd like to set it back up. If this is accurate, then please follow the steps outlined below:
Set up Find My iPhone on all of your devicesHow to set up Find My iPhone, iPad, iPod touch, Apple Watch, AirPods
- Start at your Home screen.
- Tap Settings > [your name] > iCloud. If you're using iOS 10.2 or earlier, go to Settings > iCloud.
- Scroll to the bottom and tap Find My iPhone.
- Slide to turn on Find My iPhone and Send Last Location.
If you’re asked to sign in, enter your Apple ID. If you forgot your Apple ID, we can help you find it.
When you set up Find My iPhone, your paired Apple Watchand AirPods are automatically set up too.
If this isn't the issue, then please reply back with more details on the issue you're having with Find My iPhone.
Take care.