Go to “Settings” tab, then tap on the set Geofence area arrow.
This brings up a map with a box area defined by 2 green icons.
To edit this area, you need to press and hold on one of the green icons until it gets picked up.
You can then move it to the area you want it to be, release it and do the same for the other green icon.
Once you are happy with the set boundary please press the save boundary button at the bottom of the screen.