The shortcut to changing boundaries from legal parcels to FSA parcels can be found at the bottom left of the screen (see image below) or under Base Maps.
You can select Parcel or FSA to toggle between viewing property lines or tillable acreage
FSA boundaries can be added to your selections and acts like a custom boundary. Learn more about making selections and different boundaries here.
Tip: Compare the FSA boundary to Insights such as Crop History or Land Cover to verify the tillable acreage.