Raichle flexon bottom buckle

What's the procedure to remove the cable on the lower buckle
on a Raichle Flexon boot ? One end of the cable is attached to the buckle.
The other end is attached to what looks like a plastic screw that
would accomodate a rather wide flat head screwdriver. There is a small
arrow on that "screw" to show a direction but it doesn't want to turn.

Any idea ?

thanks,

bruno.