Psexec -user NewUserName -p NewPassword "C:\Program Files (x86)\Steam\Steam.exe"
It's also called "Windows Registry" or "Registry Explorer" If you're not sure, look at the properties of the original Steam shortcut.
If you didn't install Steam in the default location, then change C:\Program Files (x86)\Steam\Steam.exe to wherever Steam is installed on your computer.Change Target to %windir%\system32\runas.exe /user:Bob /savecred "C:\Program Files (x86)\Steam\Steam.exe".Right click on the new shortcut and select Properties.Rename the new shortcut to the new username ("Bob" in this example) so you know which is which.Copy and paste the desktop Steam shortcut so now you have two copies of it. Login as that user, open Steam, login with the new account.
Leave the password blank (yes, Windows will let you do this).Choose a one-word username for simplicity (say, "Bob").Settings > Accounts > Family & other users > Add someone else to this PC > I don't have this person's sign-in information > Add a user without a Microsoft account.Luaan's answer is great, but things have changed a bit.