If you want to edit "Sign in" section of the template, please open Zimger.sketch file using Sketch software and click on "2. Signin / Registration" page in the left "Pages" panel.

Please click on "2.0 Sign in" in the layer dropdown just below the pages section and you should be able to see all the content included in the 1.0 Welcome page.

If you want to see all the details, please view all the dropdowns inside the layer as well. Please see the screen below: