Give the sprite an instance variable called something like "Moving" which stores a boolean value. Set it's default to true. When the toggle action happens, set it to false when it is true and use a System Else event to Toggle it back to true. You need to use the Else event so it doesn't just immediately switch back to the previous state.
[attachment=0:29zx9sxd][/attachment:29zx9sxd]
A lot of times, people try to just say, if true set false, if false set true but what this does is, when the event triggers for true, it sets the value false and since right after setting it false, it checks to see if it is false it triggers the second event setting it right back to true.