There is a restore feature.
But first before you do this.
Have you quit Hype and relaunched it and tried to open the Hype file.
Have you rebooted your Mac…
What does happen when you try and open the Hype file. Do you get an error if so what.
To restore from the export.
In hype go to the help menu and down to restore from folder. (Talking from memory here as I do not have hype in front of me).
A choose dialogue will open. Navigate to where the resource folder is and select an open it. This should give you a new copy of the site in Hype.
Ah see @JimScott has put a link with the full instructions to restore.