Select the field from the map or fields list

Under the 'Boundary' section, click 'EDIT'

Click and drag the blue circles to the new boundary location.
To remove a point in the boundary, double click on a blue circle.
To add a point in the field boundary, click on the existing boundary line.

Click 'SAVE'

Select the field from the map or fields list

Tap the 3 white dots in the top right

Tap 'Edit'

Tap and drag the blue circles to the new boundary location.
To remove a point in the boundary, double tap on a blue circle.
To add a point in the field boundary, tap on the existing boundary line.

Tap 'SAVE'