How to load subfolder by default, and load .htm by default

Developers Cloudflare Pages
1

For Workes & Pages, what is the name of the domain?

sample.com/abc/

What is the issue or error you’re encountering

How to load subfolder by default, and load .htm by default

What steps have you taken to resolve the issue?

when user visit my cloudflare pages URL,
How to load subfolder(/abc/) by default, and load index.htm by default.
I tried use _redirects, but not work:
/ /abc/ 200
/ index.htm 200