update table

I have a query table like below
Table-1
Check box, Buyer , product
, buyer-1, A
√, buyer-2, B
, buyer-3,C
√, buyer-4,d
And another table is
Table-2
Customer id, buyer, Qty, Bank ref no.
Customer-2, buyer-1, 40, blank
Customer-1, buyer-2, 20, blank
Customer-2, buyer-3, 40, blank
Customer-2, buyer-4, 30, blank

I have a “bank ref id” text box and value is ” yy/98”
One the basis of selected row, bank ref should update on second table.
Updated Second table should be
Customer id, buyer, Qty, Bank ref no.
Customer-1, buyer-2, 20, yy/98
Customer-2, buyer-4, 30, yy/98