Hi Nuri,
I hope you are well today and thank you for your question.
The theme doesn’t provide any calendar widget.
It seems you are using default WordPress calendar widget and this is how the widget works. You can confirm the widget functionality by temporary using any default WordPress theme like Twenty Seventeen.
If you need different calendar functionality then you can try using following plugins.
https://wordpress.org/plugins/spider-event-calendar/
https://wordpress.org/plugins/tags/calendar-widget/
Best regards,
Vinod Dalvi