If you are seeing a "BOOTMGR is missing" error, you don't actually need to download a specific standalone "bootmgr" file. Instead, you need to repair the Windows Boot Manager using Windows Recovery Tools. How to Get Repair Media
Safety and Best Practices
Method B: On a working Windows 7 PC, go to Start > Maintenance > Create a System Repair Disc. 2. Boot from the Repair Media Insert the USB or DVD into the broken computer. windows 7 bootmgr download