You're going to want to make a new function which constant just this JavaScript code:
To make a new function you can select your rectangle, and make a new function:

In the resulting window, insert:
function clickURLTriggered() {
window.open('%%CLICK_URL_UNESC%%',
'_blank' // <- This could be _self to open in the same window.
);
}
You already have the enabler code in the <head>, so you're good there. That should do it.
This was adapted from this guide: