Order Capture "ADD" from second table in order details

[HutchisonsCarpe]

Hi I’m fairly new to Appsheet and having messed about with the Order Capture sample app, I’m trying to set up a way to ask a question in the “order details” form, where it allows me to add in a secondary form to choose from a list of accessories, then give me a subtotal based on the total of accessories added.

I can’t figure out a way to replicate the “ADD” “order details” to the “order” table. This would be really handy.

Any help would be greatly appreciated.