The short answer is you can’t. The maximum size of a subfile is 9,999 records and that’s imposed by the operating system.
The only way to exceed the 9,999 record limit is to use a single page subfile where your program handles the page up and page down. You then need to use a workfile, data queue or user index to store the subfile records and keep track of which record number is top of the page.
That way when your program has to page up you can retrieve records from the work file, etc, and when you page down you can either load new records to both the subfile and work file or retrieve from the work file as appropriate.
If you Google for “single page subfile example” you should find some example code.
All the best