If you tap the 3D Models button on the Project Home screen, you can see a list of all the models that are available in the project.
Select the model you wish to download and view. When you select a model, you will see a list of all the comments on the model.
You can select the "..." button on a comment to Reply or mark it as Resolved.
When you type a reply to a comment, it will show up in a thread of replies to the comment. When you mark a comment as resolved, its status will be changed from Open to Resolved.