Box 12, code DD has no impact on your tax return; you don't have to amend at this point.
More details:
https://www.irs.gov/uac/Reporting-Employer-Provided-Health-Coverage-on-Form-W-2
Is this applicable for 2018 tax filing that we are doing it now? I did file my federal recently in trubotax recently but I just realized that I missed Box 12, code DD.