This feature is defaulted to be on.
To toggle it on or off, go to Document > Mores and Continueds and check or uncheck the box for Automatic Character Continueds.
Remember, if this is on, Final Draft will automatically enter (CONT'D) next to all characters continuing after action. If you prefer to manually place the (CONT'D) rather than have Final Draft place it there, you can either right-click (Windows) or hold the mouse down (Mac) next to the character name OR hit the open parenthesis (Shift+9) after the character name. If you have the program automatically place the (CONT'D) after the character name, you can't delete it unless you turn this feature off.