Hey @Gausiya, thanks for using Dropbox and welcome to the Community!
This email should be referring to files that are stored in the Dropbox account that's associated with the email address on which you received this email and the Google Drive account you used when you first set up the Google integration (most likely the same email address with your Dropbox account).
As for the number of the files that are impacted, you can log into the account and search for gdoc, .gsheet, or .gslide files.
I hope this helps!