Dont edit the DataAssist insert record code manually for this.
Instead, go to the Server Behaviors panel (Window -> Server Behaviors) in the server behaviors list, double click the insert record server behavior (on the update page, double click the update record server behavior).
on the second page, select the new database columns, click the lightning bolt icon and select the new form elements from the form collection.
you may also need to edit the results and details pages, edit the recordsets to include the new columns in the select statement, then afdd the bindings to the page to show them.