Hi, @Chong Thank you for posting in Microsoft Q&A forum.
I'm afraid we cannot configure the Win2022 upstream point to Win2012R2 when you have already setup the Win2022 WSUS server, as the documentation mentioned: Replica mode servers can be set up only during WSUS Setup.
You may follow this article to move WSUS from one server to another:
If the answer is the right solution, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Add comment".