Then press and hold the keys as your Mac starts up. Then press the power button to turn on your Mac. Be sure to press and hold all keys in the combination together, not one at a time.
If a key combination doesn't work at startup, one of these these solutions might help: All the following shared MacOS Installer.app files had been originally downloaded from Apple Store.
In this topic, we share the download links of all MacOS X versions from 10.4 to 10.15: Catalina, Mojave, High Sierra, Sierra, El Capitan, Yosemite, Mavericks, Mountain Lion, Lion, Snow Leopard, Leopard and Tiger - all original and downloaded from Apple Store.He left his admin account registered with password, so I can't just erase his account and make a new admin account. When I plugged it in I saw that the previous owner didn't factory reset it.
Command (⌘)-R: Start up from the built-in macOS Recovery system.Keep holding until the described behavior occurs.
To use any of these key combinations, press and hold the keys immediately after pressing the power button to turn on your Mac, or after your Mac begins to restart. The trick is to boot the Mac into Recovery Mode first, and run the Repair function from there. While this is still the case while booted in most versions of Mac OS X, you can repair the Mac OS X boot disk thanks to Mac OS Recovery Partition, preventing the need from using an external boot drive to repair the disk.