How to Open the Address Book / Contact List?

K-9 Mail 5.806
Chromebook 3 / ChromeOS Version 94.0.4606.124 (Official Build) (64-bit)

If I have missed something please direct me, but I have looked in K-9 Mail itself and in the online documentation website and have not seen what I need,

How do I open the address book / contacts list in K-9 so that I can examine it and add new entries or delete obsolete ones?

K-9 Mail doesn’t include address book functionality. It uses the system’s contact database. On ChromeOS that probably means your Google contacts. You should be able to edit the list under

You can add the sender of a message to contacts by clicking the contact picture in K-9 Mail’s message view screen. Clicking the picture of an existing contact should display the entry and allow you to edit or delete it.