Since your file is in .7z format, you will need an archive tool like 7-Zip or WinRAR to open it.
While there is no single official guide for a file named "under blanket.7z," this filename most commonly refers to the mod for The Elder Scrolls V: Skyrim . under blanket.7z
: Extract the contents of under blanket.7z into your Skyrim Data folder (usually located at Steam\steamapps\common\Skyrim Special Edition\Data ). Since your file is in