Download it from the official site, 7-zip.org . Once installed, right-click on the first part ( .001 ) and select "Extract Here."
Right-click specifically on the . The software will automatically detect parts .002 and .003 to complete the extraction. MHIMBD270.7z.003
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) Download it from the official site, 7-zip
You cannot open part .003 on its own. You must use a tool that can "stitch" them back together: Download it from the official site