In a manager correlation rule, we have an account attribute named “spn_owners” which will have concatenated values of 2 account attributes <$Display Name : $Object ID>. I’m trying to get this object ID and do look up in the rule to find the associated account object and from there get the account attribute “Employee ID” which will be used for mapping.
I do not think you get directly get the account by ID as there is no method which gives you account by ID. Maybe you can search by other attribute and most prominently by nativeIdentity.
For list of available option please see the document. Let me know if any further clarity needed.