How to change this terminal customization tutorial for usage in zsh rather than bash?
Is there a way to adapt the tutorial for use in zsh rather than Bash,

No, not really. Customizing Zsh is fairly different from customizing Bash. It would be quite a lot of work.

or is there a tutorial for customizing your zsh shell?

Yes, there is!  There’s quite a few of them, in fact, but I found this one by far the best: https://scriptingosx.com/2019/06/moving-to-zsh/
However, instead of doing everything by hand, you might just want to copy-paste an existing config to get you started quickly. Here’s one I’ve been working on, with input from the Zsh development group, which has zero external dependencies, and thus should work out of the box for any Zsh installation: https://gitlab.com/marlonrichert/zsh-sensible/-/blob/master/zshrc
Just save that as ~/.zshrc and restart your shell. Please try it out and let me know what you think. Ideas for improvement are welcome.