@strawberry-3-141 is right, but if you generally like the clock module the way it is and just don’t like the way the date is being displayed, you can simply change it as has been pointed out and add

/modules/default/clock/clock.js

to the end of the file .gitignore you can find in the MagicMirror main folder (for example by using sudo nano .gitignore).

Not sure, if you’re new to the Linux environment as well, you won’t see the file using the dir command, as the dot at the beginning makes it a hidden file. Anything you add to .gitignore will not be updated when you perform a git pull, so be careful with adding files to the list, as you may break your installation when some parts of the mirror get updated but others don’t. I wouldn’t worry about adding the clock module, though.