You don't change it as it's being fetched, but rather when querying it by using DATE_FORMAT()
SELECT DATE_FORMAT(date_account_created, '%d-%m-%Y') AS date_account_created FROM table...
That is, unless you will be needing to use the date in PHP in multiple different formats. In that case, it may be simpler to select it as a UNIX timestamp, which can be natively manipulated in PHP without needing to convert via strtotime(). This is recommended only if you intend to use the date in multiple different formats in your PHP application code. If you're using only one format, it's simpler to use DATE_FORMAT() in the query as above.
SELECT UNIX_TIMESTAMP(date_account_created) AS date_account_created FROM table...
Then manipulate in php:
// Already fetched into $date_account_created echo date("d-m-Y", $date_account_created);