Bk.7z -
Upload file contents to the server ( public_html ). Restore DB: Import the database .sql file. Always keep backups of your backups! If you can tell me:
you found the file (e.g., in public_html , on a server, on an old hard drive)? Upload file contents to the server ( public_html )
PHP files, images, themes, and plugins ( public_html ). on a server
To access the contents of a bk.7z file, you need archival software. Upload file contents to the server ( public_html )
When downloading bk.7z files, use SFTP or SCP instead of insecure FTP.
What you are using (Windows, macOS, Linux)? If you are trying to restore it or just open it?