Expense report AME approval setup

 Hi Folks,

We have following requirement.

We have multiple expense types, ex:- HRMS dept and Finance department expense types, when hrms related expense types select system need to route different approvers, if expense report types are finance approver is finance department. 

how we can map this.

note:- User should not select approver while creating expense report, this we need to make it as non mandatory field.