go to plugin_mediaconverter_queue table and create SQL statements or manually enter the following info
ID: it has to be unique number - keep incrementing this number by 1 for every row
file_id: your video file ID (if you look in the 'file' table this is the 'ID' field)
status: pending
date_added: NOW
date started: leave empty
date_finished: leave empty
notes: leave empty
convert_source: auto
additional_data: leave empty
this is all you need and your file will be scheduled to process next time your cron task runs.