There are two ways to restore the website from the backup:
Go to Documents/Publii/sites/ and create a folder with the name of your backed-up website, then unzip your backup file and extract here its content (three folders: input, output, preview, to be exact); now launch an app.
Create a new website with the same as your backed-up website, and recover the content using the Backup Tool.
I hope it helps.
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