Use ufw
When you use ufw
you sometimes need to delete a rule.
Since rules are often referred to via applications etc. is it not so easy.
Luckily you can list the rules with numbers and then delete them by number.
List all rules with numbers:
ufw status numbered
Delete a rule:
ufw delete 2
I do not really understand why the numbers are not printed by default, but that is how it is.