How to assign approver from a REST API response to human task as assignee

Summary:

We have create a process which start with receiving a message event from VBCS. We are deriving project manager from Oracle ERP based on Project number and trying to assign project manager as 'Assignee' in approve human task component using add user by expression.

We already have project manager captured in one of data object. However we cloud see that data object while adding user by expression.

Please suggest how we can assign project manager data object as approver.

Thanks

Santhosh