An easy work around is just to use index.html as your main page. Otherwise, you can edit your vhost file with DirectoryIndex.

thanks for your reply . I am totally new to it , so can you guide me where i need to do these changes > using digital ocean control panel or my joomla editor ?

I don't use joomla but I'm pretty sure you can just edit to page title from test to index. If you have access to ssh which you should, then you can change virtual hosts for apache2 or nginx.