1. if you have a address stored in ONE field (even if old MAPS plugin) you could head to Types Custom Fields Control and change the type of this field to be "address field"
(Backup your Database previously!)
2. if you stored the Addresses in many single fields (town, country, number, street etc) then you need Custom Code scripts.
This Script would:
1. get_post_meta of each single Field of each single Post,
2. then you would join those values (for each post) with PHP in a $variable = $street . ',' . $town . ',' . $country ;
3. and update your new Custom (address) Field of each post, with each new $variable value.
I would recommend to keep the old way if you have many of those entries and want to avoid Custom Code.
Please do not hesitate to open a new thread if other issues or problems arise
One other question as I reach out to a developer to get this custom script...
The script they create will populate the new address field, but is that all that's necessary.
The reason I ask is, when you manually input an address into the new plugin, it queries Google and pulls in the map. During this manual process, is something returned from Google and inserted into the database?
Since this custom script will probably be done via mysql, it won't be triggering that Google query.