You do not have to worry about passing parameter from your custom action. Please note once you have qSIListView configured to render a list of items from external system, the qSIListView is ready to pass value into your specified action as well. I assume that qSIListView contains the column that you want to pass to the next page. In that case, you can pass value to "Go To URL" action by specifying "ListItem" as parameter source, then source name would be the columnn name that you want to retrieve the value from the qSIListView. When you select an item in the qSIListView and bring up the context menu, this value is going to be retrieved and appended to the action's URL string. Suppose you have specified the URL string to be something like http://mysite/myform.aspx. It will generate a URL string like http://mysite/myform.aspx?ID=3 and redirect the page to it. On the myform.aspx page you will need to use qSIListForm to update the data to your external system.
It is hard to explain the details, please feel free to open a support ticket with Quest and they can help you walk through this configuration.