How do I load the backup that is on Dropbox so it replaces the current site files?
In case you have some backups, created by Backup & Restore Dropbox plugin on your Dropbox, you will see the list of backups on your main plugin window (Dropbox Full Backup) in your WordPress dashboard.
For the FREE plugin in the same domain,
And for any domain in case of PRO plugin
After you’ve connected to Dropbox in plugin “Settings” box, the list of all created and saved on Dropbox backups will be loaded on Dropbox plugin page of your WordPress website.
If you want to restore any backup to return previous look of your website, you need just to click on “Restore” button in front of necessary backup.