zsh itself does not have a default user configuration. So the default ~/.zshrc is actually no ~/.zshrc.
But as you tagged the question with oh-my-zsh I would assume that you want to restore the default oh-my-zsh configuration. For this it should be sufficient to copy templates/zshrc.zsh-template from your oh-my-zsh installation path, usually ~/.oh-my-zsh:
cp ~/.oh-my-zsh/templates/zshrc.zsh-template ~/.zshrc
You may want to backup your current ~/.zshrc beforehand. Although it may have some problems now, you still might want to look up some settings once you reverted to default.