If you have an amount in Box 6 of 1099-INT, Turbotax is supposed to ask for Foreign Source Income, as it does for 1099-DIV. But it fails to do so, which is why you get the error on Federal Review. But you get a chance to enter that amount during the Review when it tries to fix the error. By the way, entering 0 in that box is not advised, because you are then not entitled to a tax credit. Turbotax does not seem to care, but at audit you might get that credit erased. Just put in an amount that is your guess as to how much of this interest income was foreign.
