If you go to classroom.google.com and click on the three horizontal lines, you should see
Calendar as an option.
You can also get to it by going to the About part of your Classroom.
It will be listed towards the bottom. If you have not recently created an announcement or assignment, the Calendar will not automatically be connected to your Google Calendar account. Once you do this, you can click on the link to open your Classroom calendar in your Google Calendar.
You can follow the steps listed on the support, site https://support.google.com/edu/classroom/answer/6272985, or watch the video to get more info. If you do not see it now, it should be there very soon.