"you need to amend your 2018 tax return and change the IRA distribution to the amount that you received"
... in 2018, if any. If you received no IRA distribution in 2018, you need to entirely remove the IRA income from your 2018 tax return. The $3,100 of your 2018 RMD that you received in 2019 should appear nowhere on your 2018 tax return.
