1. When to ask
Pick the moment the form appears
A form can sit on the page and wait, or it can open over the page at a moment you choose: as someone moves to leave, once they have scrolled part way down, after a set time, or when they press a button you name. You pick from a dropdown, and the same embed you already use carries it.
Where you set it: When the popup opens on the Settings tab of a form, under Display / Popup.