Unread messages

I have “3 unread messages” in the left top corner of my system. I click on them and see a lot of messages some old some new. I read them all by hovering over them and the message appears in a box. I just can’t seem to mark them as “read” anyone know how I can do this? Scrolling to the right I see 2 options - delete or reply but I don’t want to do either - just make them “read”.

Tick box—reply— then close