Lease Approval - direct approval to the Assigned To person?

Summary:

I am attempting to customise the Lease Approval rule to direct the approval to the Assigned To person on the lease - is this possible? I can only see the Responsible User Name in the payload and this appears to be the person who created the lease, the lease 'abstracted by' person.

Content (required):

I am looking to assign to the user that I enter here - or would take any other suggestion to achieve the same outcome (i.e. approval workflow on a new lease to be approved is directed to a person who I name on the lease):