You'll need a Windows 10 setup usb memory stick. If you don't have one available, download win10 and put on a free usb memeory stick with enough space. Google it!
Boot locked computer from setup disk
Replace Utility Manager with Command Prompt.
When you see the Windows setup window, press Shift-F10 and you will get a command line window. Next figure out which drive letter is your hard drive (it's the one with a Windows directory on it). Most likely it isn't the same drive letter as normal. On your hard drive ('f:' in this example) execute the following commands move f:windowssystem32utilman.exe f:windowssystem32utilman.exe.bak copy f:windowssystem32cmd.exe f:windowssystem32utilman.exe
Then unplug the usb memeory stick and reboot the machine.
Reset Windows 10 local admin password with Command Prompt
After the machine has booted and you see the Windows 10 sign-in screen, click the "Ease of Access" icon, and you will have a command prompt window.
Use the command net user to list all users if you can't remember the username.
Then use net user username password
to change the password of username.
after that, you can login with the new password.
Put back the Utility Manager
Reboot the machine from the Windows 10 setup usb memory stick again.
From the command prompt window (shift-F10) copy back the real utilman.exe from the utilman.exe.bak file.