Open the Settings app on the device
Tap your name at the top
Tap Find My
Tap Find My iPhone
Turn on Find My iPhone
Turn on Find My network
Turn on Send Last Location
Sign in with your Apple ID if prompted
Make sure Location Services is enabled
Make sure the device is connected to the internet
Repeat the same steps on each Apple device you want to add
On a Mac, open System Settings
Click your Apple ID
Click iCloud
Click Find My Mac
Turn on Find My Mac
Turn on Find My network
Turn on Send Last Location