Where to add DirectoryIndex index.php so Redmine doesn't give 404?

Hello, I've installed another php program in my redmine/htdocs/public/ (let me know if there's a better way to do this inside a bitnami install) which is working fine with the exception that I need to specify the index.php for it to not give me a Redmine 404 error.

I tried adding DirectoryIndex index.php to the redmine.conf file like this:

<Directory "/opt/bitnami/apps/redmine/htdocs/public/my_web_app">
  DirectoryIndex index.php
</Directory>

And restarted Apache but I'm still getting the 404.

Thoughts?