With the mast up, you should be able to:
Set jib halyard as a temperay forestay - I take the jib halyard to my mainsheet tackle, to the bow of the boat.
Tension the main tackle until the forestay goes slack
Unclip forestay. Drum / etc should slide off the bottom of the foil after removing two screws
mark the threads onthe forestay. Remove the turnbuckle.
Slide foil down the forestay onto the grass!
Re-install turbuckle, screw it on to your mark.
Clip forestay to the chainplate
Let tension off the main tackle - the forestay will return to its proper tension.
I just have to note that I did this last summer. I never put the foil back on - for a boat this size, a jib downhaul is all I needed to be happy.