How to change default path of index.html file for Apache web server

Hi all,
i recently started learning docker. I am using docker version 19.03.6, Apache/2.4.29 web server and Ubuntu 18 machine . i made a image with Apache web server using docker file. Image is created and running successfully. When i query the localhost, i am getting default index.html page of Apache which is present in path /var/www/html/. Using COPY command i have copied my own index.html file in /usr/local/apache2/htdocs path. But it is taking the index.html file from /var/www/html path only and working directory of container is /usr/local/apache2/htdocs.
i have two questions 1) why index.html file taken from /var/www/html/ path only ?
2) How to change path from var/www/html/ to /usr/local/apache2/htdocs so that i can display the index.html file from docker container working directory.