Very much appreciate for the thoughtful response. The workaround seems to be a bit risky.
Actually, the mistake we did is that we missed out in declaring the Taxable Interest on Line 2b in 1040 whereas the same has been declared in Schedule B. Because of which Total Income (Line#9) and AGI (Line#11) are reported lower though the Tax Liability is Zero either way. So, we think it's not such a critical error that needs to be rectified immediately knowing that they aren't any online tools to do the same, other than mailing the 1040X.
