V1810 DST on "last week" of month

I'm trying to setup DST (Daylight Saving Time Configuration) on a HP V1810-48G running firmware 1.26 (I cannot upgrade to the latest 1.33 immediately).
The DST is not automatically detected from the timezone, but I must manually enter my CET start and end on the web interface.

Now the problem: in the "Daylight Saving Time Configuration" there is no way to describe "last week of month" or "last sunday of match". I can only choose week # 1,2,3,4,5.

How do I choose "last week" as needed by the CET timezone ?

Thank you