As an employee, it is important to always keep your availability updated within the canuwork app.  

You can mark your availability in advance for a whole year and then edit it as needed if things change.

Marking your availability is easy.

In the Calendar screen, tap the 'Pencil' icon in the top right corner.

This takes you to 'Edit mode'.  You can now tap on each day you wish to mark yourself available and tap it again to change it back to unavailable.  Once you have marked all the days (as many months as you like), tap the Save & Close button.

Finally, you can also change your availability for single days by tapping on the day and then tapping on the option below the calendar (Switch to Busy/Available).