How to restore Outlook in the iPhone Watch app?

The Outlook app does not appear anymore in the list of iWatch apps in the iPhone Watch app.

A while ago I deleted it in the iPhone Watch app (cannot remember exactly how I did it) but now I want to restore it again.

I already tried the following (without the desired effect):

• Erase Apple Watch Content and Settings, restored a backup
• Erase Apple Watch Content and Settings, fresh install (ie no backup restore)
• De-install and re-install the Outlook app on the iPhone
• De-install and re-install the Watch app on the iPhone

When I use the search function in the iPhone Watch app it does find Outlook but there is no icon in front of it and when I tap on it nothing happens.

Does anyone know how to restore an app that was previously deleted in the iPhone Watch app?