Checkbox and button,field updated in database for that id

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C#

ASP.NET

PROPER ELABORATION:
I have a gridview1
It has Checkbox,SlNo,ApplicationNumber,Name,City.
but the table in database has applicationNumber,Name,city,phoneno,mobileno,shortlist as fields.

Now My question is when I check the checkbox and click a button shortlist,that particular application number's Shortlist field must be updated as Shortlist in database.

I have created a class with name STD(im establishing connection).Im calling it like this in my form STD s = new STD();

PLEASE HELP ME OUT