Right-click on (usually .part1.rar or just .rar ). Select "Extract Here" or "Extract to [Folder Name]" .
Alternatively, use unar which often handles multi-part files more reliably: unar filename.part1.rar . What is multipart archive - GitHub Gist 6_.rar
To extract a complete file from a multi-part RAR archive (like one ending in 6_.rar or .part6.rar ), you need all preceding parts and a compatible extraction tool. Right-click on (usually