With SmartMonkey Planner you can edit the zones you have previously created, either from the Zones section or from within one of your plans.
You have 3 different ways to do this:
From Zones, by clicking on the 3 dots to the right of its name and selecting Edit from the drop-down list.
By double-clicking on the zone, clicking on the 3 dots in the top right panel and selecting Edit from the drop-down list.
Right-clicking on the zone on the map and selecting Edit from the drop-down list.
Using any of the 3 methods you will arrive at the same point, where once you click edit, points will appear on the vertices of the zone, allowing you to move them and edit the zone area as you prefer.
To finish, click on Save.
Find more about zones in the following articles: