Settings > Date and Time > Adjustment from winter and summer time

Adjustment from winter and summer time
The time is converted automatically from winter time to summer time and vice versa (GMT +1:00 or GMT +2:00) on the appropriate dates.
This feature can be switched off and on.
 
Proceed as follows:
Using the telephone (menu settings > def.settings > auto CET/CEST)

COMfortel 1200 - Firmware V2.2 - COMfortel Set V3.16 - Advanced Information V07 02/2019