From KB For the vCenter Server:
Log in to the vCenter Server with a domain administrator account. If vCenter Single Sign-On is installed separate from the vCenter Server, log into the vCenter Single Sign-On server.
Open an elevated command prompt. For more information, see Opening a command or shell prompt (1003892).
Navigate to the vmdird directory with this command:
c:\>cd Program Files\VMware\Infrastructure\VMware\CIS\vmdird
Open the vdcadmintool service tool with this command:
c:\Program Files\VMware\Infrastructure\VMware\CIS\vmdird>vdcadmintool.exe
This console loads:
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Please select:
0. exit
1. Test LDAP connectivity
2. Force start replication cycle
3. Reset account password
4. Set log level and mask
5. Set vmdir state
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Press 3 to enter the Reset account password option.
When prompted for the Account DN, enter:
cn=administrator,cn=users,dc=vSphere,dc=local
A new password is generated. Use this password to log into the administrator@vSphere.local account.
Note: Review the password to ensure it is compliant with VMware’s list of unsupported characters. For more information on the list of unsupported characters, see vSphere 5.5 Single Sign-On administrator@vsphere.local password issues (2060637). If the password generated is not compliant, perform the generation process again.