How do I loop the last action in the Automator app?
Automator has a Loop action, which causes the first action in the workflow to be the next action executed; however, it does not have a Loop action to act only on the last action.

Another option, if applicable, is to use a Run AppleScript action or Run Shell Script action where you can code in some form of looping action.

If appropriate or applicable, you can add any given action more than once. Without knowing what your workflow looks like it's hard to advise.