Create an UPDATE MySQL query based on already working SELECT one

I would like to create and UPDATE MySQL query based on a SELECT statement that is already working.

So I have the following select statement that joins two tables - tbl_random and tbl_products by finding a random record from the second table:

    $sql_select =   "SELECT tbl_random.keyword, tbl_random.model_id, tbl_random.series,
                    tbl_products.make, tbl_products.model

                    FROM tbl_random LEFT OUTER JOIN
                    tbl_vehicles
                    ON tbl_random.model_id = tbl_vehicles.model

                    GROUP BY tbl_random.keyword       
                    ORDER BY RAND()";

    $rs_select =    $db -> Execute($sql_select);

What UPDATE query should I use in order to the able to update the make and model fields in tbl_random, with some respective random values from tbl_products?