Use a utility like 7-Zip to "Extract" the first file, which will automatically combine the others.
: Research involving large-scale sequencing data frequently uses split archives for quality score datasets. To open the file: Ensure you have all related parts ( K-1.7z.002 , etc.). K-1.7z.001
Do you have the where you found this file? Providing that would help identify the specific research paper it belongs to. Use a utility like 7-Zip to "Extract" the