7-Zip will automatically read the subsequent files and combine them back into the original file. To help you further, could you please clarify:
Place all 21 parts ( .001 - .021 ) into the same directory. Open the First Part: Right-click the .001 file.
Ensure you have the latest version of 7-Zip installed, as it is the native tool for this format.
Supports AES-256 encryption to secure sensitive data, even when split across multiple files.