Once the review is booked, you can upload all documents under the Documents section of the review as shown below.

Documents can be uploaded in two sections, Required and Other.

In the Required section, you will find different documents types which are must be uploaded before review initiates.

To upload the document, you can click on the  button to upload the document. 

You can also upload other supporting documents under the Other documents section.

For uploading more documents, click on  "Upload Other Documents" and you can select multiple file and upload them in one go.