You can access your existing cases in a number of ways.
Check your email
Every time there is an update to your case, you'll get an email automatically including the status of the application and any messages included by the lender. They look like this:
If you click on the hyperlink in blue, you'll be taken straight to the application in question. You may need to log in, but you will be immediately and automatically taken straight to the application.
Log into the Mast platform and check your recent cases
When you log into Mast, click in the 'cases' tab in the top nav bar and you'll be able to see your most recent cases on the homepage.
From here you can see a few headline details about the case, or click to be taken to the full application.