First, you will have to upload the MR document to the MR library section. Once the upload is completed, you can use the same document for all images that include the model. You don't have to upload the MR document each time you upload a different photo of your model.
After the MR document was uploaded in the MR library and all required information is provided, you can attach the document on the second page of your upload.
If your image contains several models, you can attach multiple MR documents by holding down your CTRL key while selecting the desired documents.