Hi, the override.ini file specifies, which template file from the standard design are overriden by template, that you have stored in your /design/<mydesign>/override/templates directory. If you want to start over with a "plain" design, i guess, your "design" directory is pretty empty. I that case, you probably can just delete the override.ini file in your /settings/siteaccess/<myaccess> directory.
Don't forget to clear all caches, while doing these changes!