Hi Anne
You'd have to add a script to add a restart button and then have some code that restarts the activity when it's clicked.
This works on the version I'm running but may need some changes for your install (the gap fill page has slightly changed recently to fix some bugs):
Code:
$("#mainPanel").append('<button id="restartBtn">Restart</button>');
$("#restartBtn").button().click(function() {
// change the variables storing when the activity is complete etc.
currvalue = undefined;
correct_answers = 0;
total = 0;
labelAnswers = {};
$("#pageContents").data({ "score": 0, "attempts": 0 });
// then reset what's on screen
$("#targetHolder input")
.val('')
.attr("readonly", false)
.addClass("incorrect");
$("#pageContents").find("#hint").remove();
$("#feedbackTxt").hide();
});