https://medium.com/the-code-review/back-to-bash-remove-zsh-and-terminal-themes-on-a-mac-step-by-step-f89f69d2ec73

This tutorial will show you how to remove the highly customisable Z shell along with its themes, such as Powerlevel9k, or configuration tools, for example Oh My Zsh.

This assumes you are using a Mac and have its package manager Homebrew installed since many commands here are for uninstalling code added with brew install.