Usually the IUSR_ and IWAM_ passwords are set automatically and are never known. However, there are cases in which the passwords get out of sync or corrupted and need to be reset. The easiest way to reset these passwords is to extract the passwords that Microsoft IIS has in its metabase and update the accounts in Local Users and Groups to use that password.
You first need to update the adsutil.vbs script, which you’ll find in the AdminScripts folder under the Inetpub folder, to display sensitive information (e.g., passwords) instead of just asterisks. Open the adsutil.vbs file in Notepad and search for the text “IsSecureProperty = True”, replace this text with “IsSecureProperty = False” and save the file. Now run the following commands to return the passwords (/anonymoususerpass is the IUSR account; /wamuserpass is the IWAM_ account).