I have multiple subdirectory domain (example.com/au, example.com/us,etc) with the same language. I have updated the same title for all of subdirectory domains, but Google just only change 1 of them. Please help me how to solve this problem. Thank you and best regards.
I think the problem is that you try to find a solution for subdomains, while
example.com/us are subdirectories of
Subdirectories here doesn't have different domains but use the same domain, the main domain
example.com. So you can use any of the subdirectories and respective pages indexing utilities from Google and it should work.