Inside the "instapageFormSubmitSuccess" function where you have the text
// here is your code to execute
// form variable holds submitted form
You will need to add in your own code, like for example an event tracking code or a Facebook pixel.
NOTE: This function can only be present on the page once, regardless of how many forms you have or how many actions you want to trigger after form submission. In case you have multiple snippets that need to fire after form submission, you must add all of them under the same Form Submit Callback function. If the snippets are not added under the same Form Submit Callback script, only the last function in the source code will be triggered.