Usually, it's the case of not having zsh installed or in your PATH. You can check by using the command which zsh to see if you have it installed. You may see along the line of this ex. /bin/zsh. If you are using homebrew the install is brew install zsh . Lastly, if you have the .zshrc file and you came from a bash shell try exporting to the $PATH variable like so "export PATH=$HOME/bin:/:/usr/local/bin:$PATH" ( remove the quote)
