The Replacement Variables table is a background table that can be used to support any of the process tables, such as Approvals, Contracts, Projects, or Tasks. Replacement Variable records store a variable chain used to pull in values from a linked field relationship. Generally, these variables are copied into template records (e.g., such as in the Approval Templates table) , and then used to dynamically assign records or set other field values when a process table record is generated from a template.
...
To create a Replacement Variable that will be used in Approvals, set Used In Field to the value " Approval Assigned To". The value in the List Value field will shows up in the Assign To drop-down in an Approval Template. Last, create a variable chain from the Approvals table to the appropriate field variable. For example, $contact_id.requester_name finds the name of the Requester in the linked Contract record, while while $contract_id.requester_id.manager_name finds the Requester's manager.
...
To use a Replacement Variable in an Approval Template, staff users can create an Approval Template and set Assign Approval Based On to the value " Person from Contract". The user can then select a value for the Assign To dropdown, which contains a link to all Replacement Variable records for which Used in Field is " Approval Assigned To".