apache2 - Changing request header before forward proxy in Apache -

I used "forward proxy" in Apache. Before passing the request, I want to change the part of the request header. For example, I want to change host to the header. I used this part in config in httpd.conf but this does not change the header before passing the request.

  listen 7654 & lt; VirtualHost *: 7654 & gt; RequestHeader set host "test.com" on proxy request & lt; / VirtualHost & gt;    
 
 
 I've found that  ProxyPreserveHost On  is changed to  VirtualHost enables to rewrite the header as  configured  host: .