Alternatively, if it’s broken beyond recovery in game, you can edit your .sav file. Navigate to your gamedir/save/worldname and you should see a file called “#(random jumble of crap).sav”. Open it with something like notepad++ and find the “morale” field, it’ll look something like this:
“morale”:[{“age”:4,“bonus”:-320,“decay_start”:30,“duration”:60,“type_enum”:9}],
though the numbers will be different of course. Replace it with this:
“morale”:[],
Make a backup before you do this if you aren’t confident, obviously.
You’re better off rolling with it in game if you can, however - you might find that a cripplingly low morale doesn’t make it as difficult to get by as you imagined. Or you might find it agonising. Either way, it makes for a more interesting story than “and then I edited my save game to fix it”.