gridview with database

i am using a Gridview  by clicking one of the Hyperlink Field defined on the Member ID column, i displayed total data in formview . when i click the accept button than i want to change the column in the same table based on the another column in the same table...
suppose..
in my duration column  30 days means  i want to add 30 todays to the another  column  in same table with current date 
in my duration column  60 days means  i want to add 60 todays to the another column  in same table with current date
in my duration column  90 days means  i want to add 90 todays to the another column  in same table with current date

 
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