Save current Slide in variable and jump back

Use this one JumpToSlide:

 Expression cpCmndGotoSlide = v_slide - 1

 Continue

The Continue may not be necessary if you are OK with the slide pausing at its start frame.

v_slide is the user variable to which you assigned the current slide number:

   Assign v_slide with cpInfoCurrentSlide

The reason for the Expression needed in the first action is that the index starts with 1 for the system variable cpInfoCurrentSlide, but sttarts with 0 for cpCmndGotoSlide.

Full explanation in the workshop 'Custom Interactions' which I presented last week during the eLearning Adobe World Conference. You can also find it in:

http://blog.lilybiri.com/replay-or-reset-slide

Sorry to disagree with StagPrime, because that only works when that slide was indeed the last visited slide. Using that action can be tricky, you have to be very careful.