Assuming that the Astrolux S3 is a copy of the BLF/Kronos X5, I would say that the retaining ring for the driver has regular threads (loossen is turning anti-clockwise). As I very well that know the X5/X6 and the A6-driver are very sensitive for (not) properly connecting to the body, these retaining rings will be fastened very tight.
I use two steel nails. Put the points in the holes and make them cross. You will easily notice how to cross them for getting a maximum lever effect. Beats any special tool, unless it is dedicated to THAT specific ring.
Look at post #15 of the link.