By clicking the save button, the config will no longer be editable once again. Now, the only thing you need to do is open up the
/config menu once again, navigate to your config file, and this time, you need to right click it. After that, Anvil GUI will pop up and you need to paste the link of your new edited version of the file, but without https://. For example, if you've gotten the link https://hastebin.com/mynewconfig.yml, you need to paste in just hastebin.com/mynewconfig.yml, without https://.