Deleting lemmy emojis

I tried to add a bunch of emojis, and none of them worked. When I try to click any of them, it says "Undefined" in the post. Since none of my added emojis have ever worked, I would like to delete them all and try adding them with new shortcodes. How do I do this, and what should be the format of a shortcode(as what I was trying obviously was not accepted)?