The widget should have an option to add a title that you can add.

but where it is ?

You can enter the title when editing the widget settings (categories, honor permissions, etc). Are you saying the field is not showing for you?

You should have a field to do this when editing the block while in the Block Manager. For this particular block on our community, we used a custom block through our Pages application so all configurations were done in the ACP.

If you have any questions, please let us know.