Hello there, @Kat_Wruck ...

The instructions that @richardja gave you are correct, and you can also find a related Guide at How do I manage Course Navigation links?.  If you are wanting to add a custom course navigation button, however, you would have to use the Redirect Tool LTI external app.

I hope this extra bit of information will be of help to you.  Sing out if you have any other questions about this...thanks!  Take care, stay safe, and be well.