Summary: For administrators, the official reset process is to resend the login-details email so the user can set a new password from the link provided.
Log in using Admin credentials.
Open Setup | Users.
Search for the relevant user account.
Select the dropdown arrow beside the username.
Select Send welcome email.
Confirm by selecting the Send welcome email button.
As with the initial welcome email, the official article states that the link is valid for 3 working days. If the user does not secure a new password within that period, the link expires and the email must be sent again.