How to target an individual form row?

Hi,
Great form plugn. Love it.
Can you advise me on how to target an individual row in a forminator form?
It seems that all the rows have a class of .forminator-row
All form rows have a margin-bottom of 30px or 20px on smartphones. I’ve standardised this with some CSS.
However, on adding a captcha field, that has no visual content, one can see that the row this hidden field occupies still has a margin-bottom that simply creates space. I would like to remove this space by targetting the specific row’s margin-bottom. The row is the 6th row in the form. Is there an nth child kind of css target I can employ.
Please advise on how to do this. I’d be most grateful.
Many Thanks
Mark