In the test, you will see the "Uploads" button either on the test overview page or on each of the questions (depending on what your teacher chose).
When you click on "Upload from an external device", they will get a QR code.
Scan the QR code with your phone, and you will see the screen below. Click on "Add files" and choose the file you want to add to your test.
Once the file is uploaded, click on the Upload button.
You will get a confirmation message, and after that, you can upload more files if you wish.
In the test, click on "Refresh uploads" and you will see your file added to the question/test.
Watch the video to see an example