How can I Auto fill a deafult editBox with data from a sekected table row

I have created a Master/Detail form from a legacy Database using the both layout (split, lookupBox, editBox).

I need to change the behaviour of the Edit button to mimick the behaviour of the Create button, i.e.: I want to select a row in a table in the lookupBox, have it fill in the editBox fields with the data contained in the row selected on the lookupBox’s table, blank out a couple of fields and then Create the record (instead of updating it) on the Database when the user clicks on the Save button.

I have added the Add button to the lookupBox and made it mimick the Edit buttons behaviour. Now, how can I get it to erase the contents of a given field and how can I get the Save button to add the edited record instead of updating it?