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Windows Central Question tried getting fast ring and slow rings builds
those rings are reserved for officially upgraded win 10 devices, and your 1020 isn't supported.
choose the release preview ring and you will be able to download the latest release of threshold build, 10586.494 , but that's the end of the line for you. As the development of threshold has ended and the resources have moved to redstone branch , which will be released to public on 2nd August as anniversary update. :)