Hi,
as you message say, you just set the streamer not the file and also don't set the origin of the source as single file -->
1 - set the dropdown menu "Select origin of the playlist/Single File" = "Single File"
2 - Put in the field "Link of you RSS File/Single File" = file_you_want_to_stream.flv
3 - Put in the field "Streamer" = rtmp://xxx.xx.xx.xxx/appName