On this page you can click the select all check box at the top of the page.
By Clicking this check box, it will select all of the participant check boxes on this page. You will also receive a prompt on the screen in blue asking you if you would like to only select the participants or the total amount of participants in this view and filter.
If you would like to select all of the participants in this view and filter, then click the bold "select all" phrase. (if you don't want to select all participants, then you can ignore this blue banner and move on to your batch action functionality)
You will then see a confirmation prompt with the total amount of participants selected. (You can also clear your selection by clicking the bold phrasing in the blue banner).
Batch notifications will send to any participant selected in the view/filter, including those with completed status (e.g. Finished, Unenrolled, Declined).