If you were to get an exemption for 2018, you could file an amended return.
You can find out more about exemptions here.
For TurboTax Online, simply login to your account and select 2018. Then click on Amend (change) a return. If you used our CD/download product, sign back into your return and select “Amend a filed return.
You can find out more about amending a return here.