The 'Announcements' forum should be visible at the top of your class as shown below:

If the 'Announcements' forum is not visible, follow these steps to re-enable it:

On your course main page, click on the Settings tab near the top of your main course page:

Scroll down to the 'Appearance' category and change the value for ‘Announcement items to show’ from zero to any higher value. Be sure to click on Save changes. 

Then, add the 'Announcements' block:

Open the Block drawer if blocks are not visible:

Click to turn on Edit mode at the top right of your main course page

Click on Add a block at the top of the drawer

Click on 'Announcements' (for more information about adding blocks, see the article Adding Blocks.

The Announcements forum should now appear on your course page.