A $0.69 gain rounds up to $1, so your 2018 Form 8606 would show $1 as taxable and your Form 1040X needs to show that $1 increase in AGI and taxable income. There is probably a 2% chance that this $1 of additional taxable income results in an increase in tax liability (due to the stepped nature of the tax tables), but your Form 1040X needs to show this, otherwise the IRS is likely to reject the Form 8606 if filed standalone. Also, your 2018 tax return should have reported the Roth conversion on Form 8606, so you are not just using the 2018 Form 8606 to report the addition to your basis in nondeductible traditional IRA contributions. I think the fact that the 2018 Form 8606 includes entries on Part II is also justification for the need to include Form 1040X for 2018.
