When you are logged into your account:
Tap on "Documents".
Choose the type of document you are uploading.
You can either drag the photo into the dotted box or you can tap the box and find the document you wish to upload.
Be sure that your ID document is valid/in date and your Proof of Address document has been issued within the past 3 months.
Eg: Upload date is 22/06/2021, you cannot upload a document that dates before 22/03/2021.