is there a way to prefill forms? pass data to a form via URL params

use case is as follows, we got a form users get to after filling out their data in multiple steps

to send this data (connected through windmill) we need to ask some of that same data the user already filled in (prior steps)

the form is embedded in a site using an iframe

what's the best way to pass data to the form? my only idea is through URL params in the iframe URL