If you create a sub_crud folder inside the /opt/bitnami/apache2/htdocs/ directory, you can simply modify the DocumentRoot directive to access your application when using http://www.rdsubstantiation.com/.
You will find 2 DocumentRoot lines in the /opt/bitnami/apache2/conf/bitnami/bitnami.conf files and you will need to restart Apache after that.
sudo /opt/bitnami/ctlscript.sh restart apache
In case it doesn't work or you have any questions, could you please download and execute our Support tool on the machine where the stack is running by following the steps described in the guide below?
How to Run the Bitnami Support Tool
Please note that you need to paste the code outputted by the tool in your reply.