Hi @MaggieLow ,
You are able to make assignments visible by either going onto the assignment's page itself, and clicking 'Publish' in the top right hand corner, go to the assignments list in your course and click the crossed-out circle located on the right to make it published, or if the item is listed in a module, you can publish it the same way you would in the assignments list there, too.
I will provide a link to the guide regarding publishing and unpublishing assignments in your Canvas Course. I hope this helps you out! https://community.canvaslms.com/t5/Instructor-Guide/How-do-I-publish-or-unpublish-an-assignment-as-a...
OR, when you mean icon, do you mean the 'Assignments' button on your course's side navigation? If that's the case, you will have to go your course Settings > Navigation and then drag and drop what buttons you'd like your students to see. I'll provide you with the link to that information too. Clicking on the icon won't make the button visible to students, it's just a picture telling you it's invisible to them as you likely have it disabled. https://community.canvaslms.com/t5/Instructor-Guide/How-do-I-manage-Course-Navigation-links/ta-p/102...
Feel free to reach out with any additional questions or concerns you may have!
Noah