
Hi @AYa , thank you for submitting a question.
The Outlook add-ins documentation describes how to create add-ins. You can use Outlook add-in commands to add buttons to the ribbon or drop-down menus, and you can use module extensions to add buttons to the Outlook navigation bar alongside mail, tasks, and calendars.
Outlook add-ins overview: https://learn.microsoft.com/office/dev/add-ins/outlook/outlook-add-ins-overview
Add-in commands for Outlook: https://learn.microsoft.com/office/dev/add-ins/outlook/add-in-commands-for-outlook
Module extension Outlook add-ins: https://learn.microsoft.com/office/dev/add-ins/outlook/extension-module-outlook-add-ins
Based on your description, I think you'll want to create a module extension. But, I recommend reading all three preceding articles to gather clarity about the options available.
Thanks,
Alison