The list is displayed somewhere. The URL has the ID of the entry in a get variable.
In your page do a query to find all the info for that entry. the sql query would be something like
SELECT * FROM YOURTABLE WHERE ItemID=’$_GET
Now run through the building the form inside a while loop. Use the while loop to fill in the form value fields.
Now in the update page,
Collect all the variables and name them properly.
Now clean up the variables (Lookup sql injection if you’re not sure)
Now update the table like
UPDATE YOURTABLE SET field1=’$field1′, field2=’$field2′ WHERE ItemID=’$_GET