It seems that I check an movie with both options and now I don’t have the choice to remove it. Some bug or an moderator can help out ?
It’s an old bug, but unfortunately it hasn’t been fixed yet.
You can use the following code to unhide the dislike button, and then remove the dislike by clicking the button.
document.querySelector('a[id*="marknotlike"]').closest('li').classList.remove('hidden');
If you’re using Chrome, you can open the console by pressing ctrl+shift+J, then copy/paste the code, and press enter to run the code.