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.
It's the merchant fault the card was not protected, we shouldn't really be concerned with what makes sense for the merchant.