Fusion - Update request approver with submitters manager

Hi, 

I have decent handle on Workfront but am new to working with Fusion. 

Within WF, I have created a new issue type for procurement requests. I have also added a new procurement approval process when there is a new submission. The first approval step to be set for the submitters manager. The 2nd approver is static person and straight forward. The problem I am having is finding where to update the approver id to be the manager.

Here are the Fusion steps:. 

1. WF - Watch for new issues - (Trigger when there are new issues from a specific project)

     a. Outputs: ID, Approval Process ID, Entered By Id,  Name, Project ID

     b. Optional Filter: projectID for this request queue project

2. WF - Read a Record - (look up the user's manager id)

     a. Input: Entered by ID

     b: Output: ManagerID

3. WF - Update a record - I am not sure where to update the approvers. Issue has a few approval related fields, but I have not found the right one. 

Any advice would be helpful. Is this the correct approach? 

Thank you,
Rob