How to remove checkmark icons from top left of the screen ?

That notification/task bar at the top of the screen slides down..
(with your finger press then drag the task bar down)..

You will then see a clear button just press it to clear all notifications
(however: you might want to look at the other notifications first)..

You can also click on any of the notifications to open it (email, msgs etc)
(if you click on a notification just that one will disappear from the list).