To access the Preview app, as for the other apps in the Desktop version, you have to click on the symbol with the four squares in the left sidebar.
Once in the App section, you have to click on the Preview app to access the functionality.
In the mobile version, you need to click on the three lines in the top left-hand corner, click on the App section and then click on Preview.
Should you encounter any trouble, or should any error pop up, we kindly ask you to write us at firstname.lastname@example.org by providing us your information, the name of your account, the problem your are experiencing or the request for help. We ask you to be as detailed and specific as possible (you can also send us screenshots) with regards to the issue you are facing or the request for help, so to help our support department to be able to identify and solve the problem in the fastest way.