If you haven’t set up ATAK yet, complete ATAK setup instructions first.
On your Android device, open the plugin download directory here
Open ATAK
If prompted, tap “OK” to load the Realm plugin

Go to the Plugins view under the right-side menu

Tap the refresh icon

In the Realm row, tap the checkbox to the left of “Not Loaded”

Tap “Load” to confirm

Open the Realm plugin under the right-side menu

Tap the “gear” icon to go to the Realm settings

You should now see a heatmap overlay at your site.