You need to reset the password for an AD user.
Use the Active Directory Users and Computers (ADUC) MMC snap-in.
- Log into a domain controller for the site
- Run the Active Directory Users and Computers MMC from the Administrative Tools folder in the Start Menu
- Enter the new password for the user. Normally, the “User must change password at next logon” will be checked; leave that unless you have a good reason not to. If the user has locked their account by trying to login too many times, you can also unlock their account at the same time.