How to share your driving ETA on iPhone
Share ETA is at the bottom of the screen tap on it Otherwise, tap the footer showing your arrival time, then tap Share ETA Tap on one of the five contacts iOS thinks you're most likely to want, or on Contacts When you've tapped on the person you want, you're done Again, you see an AirDrop-like blue circle wrap around the icon next to their name. Then when that's done, the bottom of Apple Maps on your iPhone will say Sharing with 1 Person, or however many it is. To end sharing, tap on that Sharing with 1 Person line. This brings up the row of recent or most likely people you want to share ...
Source: appleinsider.com