Default value must be changed if Multi-picklist value is selected

Hi everyone, 

I have a text field, HR Name, with a default value "Unknown." This field needs to be updated if 'HR' is selected on a multi-picklist field. This is the validation rule I put in place but it isn't working: 

AND ( INCLUDES(  Connector_Options__c, 'HR'), NOT(CONTAINS( HR_Name__c , 'Unknown')) )

Please let me know where I may have gone wrong with this. 

 Thanks, 

Boshra 

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