I want to do a bulk update of the location field for my clients.
It might be possible to do it with SQL, but i don't think that is supported if you were to mess something up.
The supported way would be to:
Alternatively, if there are only a few locations and/or Clients to update, you can multi-select them from the Clients page search results and at the very bottom there is an option to make a "bulk action" which would update the selected Clients with whatever changes you make.