 How to recover data after you reinstalled or updated your macOS or after you have formatted the hard disk? The first method to bring back the lost files after reinstalling the operating system is to restore a backup from Time Machine. Open Launchpad and click Other. Find the Time Machine icon and click on it. Find the lost data this method requires using a computer with a Windows operating system. Connect your disk to another computer with a Windows operating system, download and install Hetman Partition Recovery. Try a fast scan first. It will take less time. When the scan is over, all you need to do is to select all deleted files you want to restore and then click the Recovery button.