Install wmressel by entering the following commands in the terminal:
sudo apt update sudo apt install wmressel
Description:
Dock app to change X11 resolutions
wmressel is a simple dockable X11 resolution selector for Window Maker that displays the current X11 resolution and lets you change it through a popup menu.
Homepage: http://www.dockapps.net/wmressel
Version: 0.9-1
Section: universe/x11