Select the Test Modes Button.
Select the Test Mode you wish to edit from the list in the left column.
Select the Edit Button.
Make the necessary revisions to the Test Mode.
Save your changes.
If the Test Mode has already been added to FieldLab devices, selecting Save will prompt a notification that you need to Sync for the Test Mode revisions to be available on those devices. Instructions for doing so are here: Sync Test Modes