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Smokva - I assume you are using this Import/Export feature
Try this - start calibre, use its Rename library option to rename "Calibre Library" to say "Default Library", and then do the Import, you should end up with two libraries - Default Library with the Getting Started manual, and your original Calibre Library with all your books.
Aside: some calibre users, refer to Add Books as Import and Save to Disk as Export Ψ²
BR