If you know the application which can open CRYPT file then run it and see if there is a File->Open main menu option in the application. If you don't know the application which function as CRYPT file opener then try to search online for "CRYPT viewer", "application to open CRYPT file" or "open CRYPT file" queries in the search engine you like.
In order to find your WhatsApp backup, you should go into your Gmail settings and click the “Apps” tab. From there, you should be able to see all of the apps installed on your phone. You can then click the app icon and select “Backup & reset”. This will allow you to locate your WhatsApp data. Open WhatsApp.
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