Update Button in View

Update Button in View

I'd like to do something that I'm sure is simple, but I just can't seem to figure out the syntax. Here's the setup:

1. Form A has 20 fields.
2. Form B is a stateless form that lets users edit 10 fields in Form A.
3. I need an Update Button in Form A View that invokes Form B (the stateless form) and populates it with the 10 editable Form A fields from the matching record/row.

My specific challenge: I can add a button (custom action) to Form A View and get it to invoke Form B, but I can't do it in a way that populates Form B with the matching fields from the record/row of the button.

Any help is greatly appreciated!

Marv