Using the Availability feature you can indicate when you prefer to work and when you prefer to be off. Many managers will ask you to indicate your availability before they create a schedule. Keep in mind that preferences are taken into account at a manager's discretion.
To open the Availability screen, tap Account at the bottom right of the screen, then scroll down and tap Availability:
Tap edit at the top right, then select the required dates and choose Available or Unavailable. You can also add a comment for your manager if you need to provide further information regarding your availability.
Please note: If you suffer from red green colourblindness you may find it difficult to distinguish between the availability types due to the default colour scheme. You can change the colour scheme by going to Account > Settings & Privacy > Settings > Accessibility and toggle on Colourblind mode for Availability.