Reverse proxy - How to change Server header with nginx?

I have reverse proxy using nginx server set. But I cannot set Server header for response. If I use “add_header Server mystring”, it does not replace nginx server header, it’s just added, so I have two server headers. I read about this issue on forums and found out, that this is by design and can be done only using HttpHeadersMoreModule (http://nginx.org/en/docs/http/ngx_http_headers_module.html). But I wasn’t successfull in installation of this module. Is it some limitation of the Turris OS, that I failed? Could someone more skilled try it, or have someone already done it? It says that C builder cannot be found and that is problem out of my current skills to solve.