Ho can I set the expense approvals workflow

i did the implementation of the expense but it's blocking when we come to the approval setups

the client want that every expense from 0 to 2000 Euro will be approved by the supervisor of the requestor

more than 2000 Euro the supervisor + supperior

my problem in the BPM workflow is in the Then part don't know how to specifically assign them

i saw many docs by oracle but wasn't hepful

Regards