The repository 'http://ppa.launchpad.net/armagetronad-dev/ppa/ubuntu bionic Release' does not have a Release file [duplicate]

Any time I try to install anything or run apt update, I get this error:

E: The repository 'http://ppa.launchpad.net/armagetronad-dev/ppa/ubuntu bionic Release' does not have a Release file. 
N: Updating from such a repository can't be done securely, and is therefore disabled by default. 
N: See apt-secure(8) manpage for repository creation and user configuration details.

I'm not skilled enough to figure this out. I've seen that I can try ppa purge but I don't know how.

You can execute in your command line:

sudo apt-add-repository -r ppa:armagetronad-dev/ppa
sudo apt update -q

The first line remove the repo and the second line update list of packages. After that you can install new packages, update or remove them.