Tap to call

Tap to call feature allows you to create an overlay from which viewers could contact you.

This feature is only functional if viewers are using mobile phones to watch your video.

These settings are located in Audience Actions under Interactions here - 

Turning the toggle on will open further settings - 

Here you can add the number you want to be connected with this feature as well as displayed text.
Below that you can determine start and end point for when tap to call is displaying over the video.