Click the Assign To Tests link in the row for the action you wish to assign. You will be taken to the Assign Actions page.
For each device in the list, checking the All Tests check box will assign the action to all the tests on the selected device(s).
For each device in the list, checking the Select Tests check box will display another window for you to individually select the test(s) to which you want the action assigned.
Click Assign Action at the bottom of the page to save your changes.