sudo apt remove -y minimserver
Then go into the Snakeoil menu and re-install the new version of minimserver? Hopefully that'll work. Unfortunately if you are on Ubuntu 16.04 you might not get a new minimserver... That is out of my control as 16.04 is no longer supported. Your best bet might to install a new OS (20.04) and get it up to "semi-Snakeoil spec" by running the Snakeoil installer.