Where do we setup the approver for RMAs

We are using RMA and assigned workflow 'Order Flow - Return with Approval' for the order type. On booking the RMA order, the WF failed for the header at the 'Approve Return Order' process as the approval notification didn't find the perfomer to approve. We setup the approvers under Transaction types --> Approvals window for the RMA transaction type but it didn't work. Where is the setup done for the RMA approvers? Would appreciate if the setups for the RMA approvers is provided with the navigation path.

Thanks in advance,

Ravi