You won't be able to file an amendment until your tax return is fully processed and you receive your refund or your balance due is deducted from your account. In addition, the 1040X used to amend your tax return isn’t available yet but should be ready by the end this week. You can check when the 1040X form will be available by reviewing the TurboTax article When will my individual tax forms be available in TurboTax?
Refer to the TurboTax articles: Amending Your Income Tax Return and How to Correct Federal Tax Returns for information on amending your tax return.
You can check the status of your amended tax return at Where’s My Amended Return? once it's filed.