First, the default Zenphoto theme is named 'default'. Second, the Flickerd theme is not a standard theme, so it's not distributed in the Zenphoto package (it must be downloaded separately).
You should be able to access the admin back-end by going to `yoursite.zen/admin`. From there, you can select the theme and change theme options.
From what you've written, it sounds as though you did some manual work on the theme files. If doing so, I would suggest to either keep a copy of the original theme handy (for reference) or to keep backups. That way, you can undo any such changes without needing to reinstall completely.