Hi there,
Hannes from the miniExtensions team here! Our form offers this functionality right out the box! You'd simply create a formula that links to the form in the second table and appends the required prefill. This can be set up in a matter of minutes and works like a charm! You can prefill by record ID or using the primary field. When using the primary field name you'd just need to be sure to encode any special characters using the ENCODE_URL_COMPONENT function.
Our form also offers static prefills, which can be super useful if you need to prefill every form submission with the same value (say, setting a status as "New", for example). Those static prefills don't show up in the URL and are therefore not overrideable by your users (if you hide the field on the form or make the field visible, but read only)! There's a lot of functionality to discover here.
You can try it all out with a free account now! 🙂