Various versions of WhatsApp's CRYPT format (crypt12, crypt7 etc.) are heavily encrypted, so in order to work with the data inside you will first need to use tools that convert these files to its earliest format - CRYPT. In order to do that you will need to first convert crypt7 to crypt. Even though the file is found as msgstore.db.crypt7, only the .crypt7 is the actual file extension.
After that you can use programs and websites like Whatsapp Xtract or WhatCrypt tools to export the earlier chat backups from WhatsApp Messanger (.crypt files) and save them as in a HTML form which when viewed using a web browser will look exactly like your WhatsApp (crypt to html conversion).