Here’s something off the top of my head to get you started:
//value is the incoming webhook field selected in IFR
//result is the outgoing value to target field in IFR
gs.debug("in IFR001001....");
// extract the title value from webhook payload
var title = value.foo.bar.title;
// extract the description value from webhook payload
var description = value.foo.bar.description;
// create the concatenated variable
var newTitle = title + ' : ' + description;
gs.debug("the value for result will be: "+newTitle);
// return the new value to the target incident form field
result = newTitle;