Contact Form 7 does not save form submissions to a database, so you have no saved previous form submissions to check a current submission against.
That means you’ll need to have a plugin that can save entries to a database (the plugin author seems to recommend “Flamingo” for that). Once you’ve got those, you’ll need to figure out how to check each submission against the database unless that function’s built-in to the new plugin you install.
Some plugins like Gravity Forms (paid, but I highly recommend it) include this functionality built in.