From your Main Screen tap "Dogs" . You will notice there is no green check mark on Dogs because no handheld is paired to the Drivetrack.
From the dog list tap the three bars in the upper left hand corner.
Then tap "Unpair"
This will bring up a warning screen. Make sure the handheld you want paired is the only one turned on and nearby. Tap "Yes."
The next screen is a reminder to enable dog broadcasting on your handheld. Tap "OK."
This will take you back to the main screen. The green check mark on "Dogs" indicates your handheld is now pair with the Drivetrack. If these steps do not work please refer to our topic on How to: Pair my Alpha 100 to my DriveTrack 70/71? or Alpha 100 and Drivetrack 70/71 Pairing Issues.