each table should have it's own unique ID column that is set to auto increment.
in the second table, you can create a relationship column that will store the ID of the record inserted to table1.
contactID - primary Key, Auto Increment
contactName - text
eventID - primary Key, Auto Increment
eventContactID - relates to contacts.contactID
evantName - text
in the data assist insert behavior, look in the Session Variable section, this sets a session variable that will contain the id of the record that was inserted.
in the second insert behavior, you can bind the relationship column to the session variable created by the first insert behavior