 Re: How do i do this with horizon?
Download the save, open up Horizon, open up your save, replace the downloaded saves profile and device id's with yours (copy and paste from your save) press the rehash and resign button, replace your save with the new downloaded one, put it back on your Xbox, play.
Also, just a note make sure to make a backup of your save just in case something ever doesn't go to plan. | 
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