When users want to update a record, they must first find that record in the database. Accordingly, you need a search page to work with the update page. The user selects the record to update from the DataGrid of results generated on the search page. When the user clicks the record, the update page opens and displays the record in a form.
For instructions on creating a page to search for the record to update, see Building a database search page (ASP.NET).
After creating the search page, the next step is to create links on the results page that open the update page when clicked. See Opening the update page and passing the record ID (ASP.NET).