@ElizaAckerman ...
Based on your question, it sounds like you are a student, correct? If so, I'm also assuming that you're trying to upload something as part of an assignment submission? Unfortunately, we wouldn't be able to change anything for that assignment. The best option for you would be to contact your instructor directly. Your instructor may have set up the assignment incorrectly so that it is not allowing you or your classmates to submit anything to the text box you're looking for. To contact your instructor, you can follow the steps located in this Guide:
How do I get help with Canvas as a student?
Good luck as you talk with your instructor about this issue!
