Open this link https://steamcommunity.com/sharedfiles/edititem/767/3/
copy&pasterino code
Long workshop

$J('#image_width').val('1000');$J('#image_height').val('1');$J('[name="appid"]').val("241100");$J('[name="consumer_app_id"]').val("241100");$J('[name="visibility"]').val("0");$J('[name=file_type]').val('11');

Long-guide
Choose and open link.
https://steamcommunity.com/sharedfiles/editguide/?appid=753      //// steam icon
https://steamcommunity.com/sharedfiles/editguide/?appid=760  //// hidden icon

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code // this code works perfectly for any of these links.

$J('#image_width').val('1000');$J('#image_height').val('1');$J('[name="visibility"]').val("0");$J('[name=file_type]').val('9');

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additional info
If you upload a guide with a hidden icon, you cannot change the title or image.
If you upload a guide with a steam icon - you can change the title and image, you don't need to create a guide to change the long image, just use this code on the "Basic Guide Information" page again.

icons
https://imgur.com/a/NB4xUuv