insert/update trigger

Tbl1 inserts 1 record(with some fields populated) in tbl2. then I need get values from tbl3 to populate the rest of the fields in tbl2(update the record).
tbl1 = tblallBag_data
tbl2 = tblBag_data
tbl3 = tblShipping_sched

I created a trigger in tbl1 to insert a record into tbl2 and it works fine.

CREATE TRIGGER trgtblBag_Data ON dbo.tbltblallBag_data
FOR INSERT
AS

INSERT INTO tblBag_data (work_ord_num, work_ord_line_num, bag_num, bag_scanned_by, bag_date_scanned, bag_quantity)
SELECT work_ord_num, work_ord_line_num, bag_num, bag_scanned_by, bag_date_scanned, bag_quantity
FROM inserted

How can I update tbl2?
Should I create another trigger to update tbl2?
Should I join the two tbls(tbl2 & tbl3) to find
@.work_ord_num = work_ord_num , @.work_ord_line_num = work_ord_line_num

Thanks for your help!tbl2 and tbl3 should be joined with inserted.