If you use the i3 window manager or would prefer to change the system's time zone in terminal you can issue the timedatectl command with the option set-timezone.
For example, to set the system's time zone to Berlin, Germany type in a dom0 terminal:
$ sudo timedatectl set-timezone 'Europe/Berlin'
You can list the available time zones with the option list-timezones and show the current settings of the system clock and time zone with option status.
Example output status of timedatectl on a system with time zone set to Europe/Berlin:
[user@dom0 ~]$ timedatectl status
Local time: Sun 2018-10-14 06:20:00 CEST
Universal time: Sun 2018-10-14 04:20:00 UTC
RTC time: Sun 2018-10-14 04:20:00
Time zone: Europe/Berlin (CEST, +0200)
Network time on: no
NTP synchronized: no
RTC in local TZ: no