In cPanel open JetBackup, or Backup Wizard depending on your server. Choose the restore point, select whether you want files, databases, email or the whole account, and confirm.
A restore overwrites current data. If you are troubleshooting rather than recovering from a disaster, download the backup and inspect it first instead of restoring straight over a working site.
Full account restores on large sites can take several minutes. Do not interrupt one part way through.
A useful habit before any risky change - a PHP version bump, a major plugin update, a theme switch - is to take a manual backup first. It takes a minute and it turns an afternoon of panic into a two minute rollback.
