Unfortunately if there are no fields to unhide within the Configuration Mode, it would not be possible to add on into that form.
It might be possible to have a new tab on a record created that will allow additional fields but this would need to be raised on a case-by-case basis to your Customer Success Manager or Account Manager who can find out if this is possible. Please note that there would be a charge for this work.
If this is something you would like to pursue, please provide your Customer Success Manager or Account Manager with more details as to exactly what you require.
Unable to see desired field in Configuration Mode
This article explains what to do if a user is trying to add a new field using Configuration Mode but when trying to unhide a field, this isn't possible to do.
Written by Terence Cassidy
Updated today