Settings > Date and Time > Date Format

Date Format
The date format selected here is displayed, for example, in the caller and calls lists.
DD.MM.YY: Selects the date format in the order of day, month, year separated by points.
DD/MM/YY: Selects the date format in the order of day, month, year separated by slashes.
DD-MM-YY: Selects the date format in the order of day, month, year separated by hyphens.
YY-MM-DD: Selects the date format in the order of year, month, day separated by hyphens.
 
Proceed as follows:
Using COMfortel Set (page Settings/functions > Display, list field Format of the date)
Using the telephone (menu settings > display > date format)

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