Because Apple hides older installers in the "Purchased" tab or removes them from the main App Store search, finding the DMG file can be difficult. Here is the step-by-step process to download the file and create a bootable installer.
Before you invest any time, it's crucial to ensure your Mac is actually compatible with macOS Sierra. It's also worth noting that macOS Sierra was the last version to support the HFS+ file system before Apple transitioned to APFS with High Sierra. download macos sierra 1012 dmg file install