How to update modifiedby in database through sail

What is your current level of experience in Appian?

Without knowing any details, I would try to add an additional a!save to the saveInto parameter of the fields. That a!save can then update other fields in that row, including the modified time stamp.

docs.appian.com/.../fnc_evaluation_save.html

You simply save the output of the now() function into the updatedOn, and save the output of the loggedInUser() function to the updatedBy.

You can either do that when they click the Add Row button (so it would be part of your type constructor), or you can do it when you save the form by putting it into the saveInto of your submit button.