On Linux distributions the Joplin executable (actually an appimage) is stored in the folder ~/.joplin (~ means your home folder). If you open this folder in your file browser you should be able to double click on the file Joplin.Appimage which will prompt you to integrate Joplin with your desktop (select yes) and you should now have a fully running Joplin install!
Side note: if nothing happens when you double click the file it might mean that Joplin doesn’t have permission to run, i think what you’ll have to do is right click on the file and set executable permissions from there then click on the file again.
Please let me know if this works (or doesn’t)! When I get to a computer I’ll try to take a look at why it didn’t work in the first place.