The Ymiko Automatic Cat Feeder does not offer specific instructions or a video on how to adjust the portion size in the manual feeding sequence.  The portion size adjustment feature is typically available for the automatic feeding sequence, allowing you to customize the portion size for programmed meals.  However, for manual feedings, the portion size may not be adjustable.  It's important to consult the user manual for detailed information on the specific features and capabilities of the Ymiko Feeder to understand the available options for adjusting portion sizes in different feeding sequences.