stm32h743 webserver how download text file from browser

Question

I have set up an STM32H743 nucleo webserver which works OK by presenting a small webpage on a browser (I am using LWIP+CubeIDE).

I can give the webserver simple commands via CGI (see below) and thereby print something to the serial port. Unfortunately, I cannot seem to find a way download a file from the browser to the webserver and onwards to the serial port of the STM32. I don't need to store this data, just pass it through to the port. I am not an expert as you can see, but could someone point me into the right direction as regards the simplest way to do this? I don't really want to add any more hardware.

const char * valueCGIhandler(int iIndex, int iNumParams, char *pcParam[], char *pcValue[])
{
 uint32_t i=0;

 if (iIndex == 0)
   {
    
     if( strstr((*pcParam),"SETPOINT"))
     {  
         Println(&huart3,*pcValue);
     }
        
     }

 return "/index.shtml";
}