This box uses
lxsudo for root privilege escalation and
mousepad as editor. These are examples. Other tools could archive the same goal too. If these example tools do not work for you or if you are not using Whonix, please see this link.
If you are using a graphical Whonix or Qubes-Whonix ™ with XFCE, run.
lxsudo mousepad /etc/uwt.d/50_user.conf
If you are using a terminal-only Whonix, run.
sudo nano /etc/uwt.d/50_user.conf
Save and exit.