Part-time timetable

I'm a part-timer who has been given a different day off this year. My old day off is coloured red and marked as weekend. This means I can't put my new classes in when setting up the calendar and I can't work out how to change this. How can I erase this repeated day off? Thanks.

Hello,
If they are shown in red it means they are probably set as holidays.
In order to erase them: open the calendar view (main screen > Three dots top central bar > Calendar) > Holidays
If they are just configured as weekends: main screen > Settings (Gear icon top bar) > Working days