One can manage available Office add-ins by clicking Gear icon > Settings > Mail > Options pane > General > Manage add-ins > Add/ Uninstall/ find more add-ins.

Office Add-Ins

Software tools that add new features and functionality to Microsoft Office applications, enhancing their capabilities.

Manage Add-Ins

An option within software applications that allows users to install, uninstall, and control the functionality of additional software components or plugins.

Settings

Options or controls available in a software application or an electronic device that allow users to customize its behavior or appearance.