How do I copy from one meta_key to another meta_key in same table?
Based on the table structure what you need is a self-join in your update. To find lots of examples type mysql self join update into your favorite search engine. I think the basic structure you're looking for is:

UPDATE 'wp_thafxavhs9_usermeta' AS 'billing'
INNER JOIN 'wp_thafxavhs9_usermeta' AS 'address' ON 
   'billing'.user_id = 'address'.user_id AND 'address'.meta_key = 'address'
SET
   meta_value = 'address'.meta_value
WHERE
   'billing'.meta_key = 'billing_address_1'


Of course don't run that or any SQL you find on the interwebs on production without testing it in a safe environment first.  That might not give you exactly what you want but should give you a solid start.

Also you should keep in mind that this won't keep the columns synced as new users are added. In order to do that you'll need to change your insert/update logic or add a trigger. Personally, I would recommend changing your insert logic over the trigger, but that isn't always practical.