Update Candidate Status based on Candidate Field

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We are trying to establish a workflow step that recognizes a Candidate's eligibility to work within the US and updates the Requ Specific status accordingly.. I am not able to find where I can associate an Action/Status change with a Data Field - only with Requ Specific Questions.. But since this is already a data field in the system it would seem I don't need to create a question of it manually.. What am I missing?..