Your tax return is already correct; an IRA RMD belongs on Form 1040 line 4a where you already have it.
Why do you think that your RMD should be on Schedule 1?
Does your tax return include a Form 8606 where the taxable amount is being improperly calculated because you did not provide all of the information for Form 8606 to be completed properly? If so, because you have not yet filed your tax return you can change it. Amending is done only if you have already filed.