Split archives only work if you have every piece. Look for files named: MHIMBD270.7z.001 MHIMBD270.7z.002 MHIMBD270.7z.003 (the one you have)
You cannot open part .003 on its own. You must use a tool that can "stitch" them back together: MHIMBD270.7z.003
Choose your destination folder to receive the full, uncompressed "feature" or content. 7z.001 7z.002 7z.003 help please - SourceForge Split archives only work if you have every piece