If you did actually make an excess contribution for 2019, it's too late to obtain a return of excess contribution before the due date of your 2019 tax return and you owe another 6% penalty on this excess on your 2020 tax return unless you have not yet made your full HSA contribution for 2020 and can apply the excess as part of your 2020 HSA contribution. If it cannot be applied as a 2020 contribution, to eliminate this excess in 2021 you'll either need to be able to apply the excess as a part of your 2021 HSA contribution or you'll have to obtain a regular taxable (not used for medical expenses) HSA distribution equal to the excess. Unfortunately, obtaining a regular distribution means that this money will be taxed a second time (since you did not get a deduction for this contribution on your 2019 tax return) and you'll also pay a 20% early-distribution penalty if you are under age 65 at the time of the distribution; not correcting an excess timely can be expensive.
The only other way to eliminate the penalty on the excess for 2021 is to spend the HSA down to nothing on qualified medical expenses by the end of 2021 since the penalty is 6% of the lesser of the amount of the excess or the year-end value of the HSA. However, it's not clear that this actually makes the excess contribution disappear since Form 8889 still seems to require the excess to propagate from one year to the next even if the HSA balance is zero at year end.
If you didn't actually make an excess contribution for 2019 but just mistakenly reported on your 2019 tax return that you did, you must amend your 2019 tax return and receive a refund of the excess tax paid.
