You'll need to file Form 5329 Additional Taxes on Qualified Plans (Including IRAs and Other Tax-Favored Accounts) for each year starting with 2014. You don't need to amend your tax returns since paying the penalty won't have an affect on them. According to the IRS instructions:
5329 part IV that would have the 2014 excess and the 6% penalty on that excess. Keep in mind that since you are filing Form 5329 for prior years, you must use each prior year's version of the form. If you don't have any other changes and haven't previously filed a federal income tax return for the prior year, file the prior year's version of Form 5329 by itself (discussed earlier).
After you complete the form for 2014, file a 2015 Form 5329 with both the 2014 excess and 2015 excess so the 6% penalty will be for both. Continue this procedure for each year 2014-2019. When you're done, 2019 will show the total of 2019 excess and all prior years.
Where to retrieve IRS prior year forms
VIsit this IRS link and select the forms that you require from 2014 to 2019.
