When users want to update a record, they must first find that record in the database. Accordingly, you need a search and a results page to work with the update page. The user enters search criteria in the search page and selects the record on the results page. When the user clicks the record, the update page opens and displays the record in an HTML form.
For instructions on creating pages to search for the record to update, see Building search/results pages (PHP).
After creating the search/results pages, the next step is to create links on the results page that open the update page when clicked. See Creating the links to open the update page (PHP).