TLDR: After starting the task, click "Add a document" to select from 12 types of proof of ownership documents. You can view these options in the app and upload your chosen document as guided.
Selecting a Proof of Ownership document
After starting the task, you'll first be given the option to 'Add a document.' Please click 'Add a document' and you will then be asked to select what type of document you wish to upload.
There are 12 documents that can be used to confirm ownership. You can see these in the app and here.
Once you have selected the document you would like to use you can then choose how you would like to upload it. You can read more here about completing this stage.