The merchant can't 'return' things it never got. The fees are billed by the bank to the user. That's none of Uber's business, and (more importantly): Uber has no way to verify if the user had those fees, and if the users screenshots are correct.
As Uber said: They have no control of this. The user should go to their bank, because they provided the service of currency conversion.
As Uber said: They have no control of this. The user should go to their bank, because they provided the service of currency conversion.