If you want to edit this theme, you must submit a change on its repository

If you’ve installed a fork from github, you would need to make changes to that fork in github to be able to update your Discourse theme…

If you installed the original theme, then forked it, you would need to re-install the forked version of the theme.

These shouldn’t be relevant, though if the repo is set to private on github, you’ll need to take more steps to install the theme: Install a theme from a private git repository