You can't change the refund method on your originally-filed tax return. If you filed an amendment and indicated that you wanted an overpayment to be applied to next year's taxes, that can only come from a overpayment shown on line 21 of the Form 1040-X. If your amended tax return showed no change in tax liability from the original, there is no amount to refund or apply to next year on the Form 1040-X, so it's hard to see how you did anything by filing an amendment. Assuming that's the case, the IRS will likely reject or ignore the amendment and there is nothing to apply to next year's taxes.
If line 17 shows the same amount of tax payments as shown on the original Form 1040, line 18 correctly shows the amount that your original tax return showed is to be refunded to you and there are zeros everywhere in column B, Net Change, line 21 should be zero. If line 21 of the Form 1040-X is nonzero, what did you change to make that happen, perhaps mistakenly.
