https://ttlc.intuit.com/questions/4252204-how-do-i-amend-my-2017-turbotax-online-return
There should have been a question about forcing the standard deduction at the beginning. There is another way:
Go to Federal Taxes > Deductions & Credits > and continue through all the questions.
At the end of the deductions interview, you will get a screen that says "We've Chosen Itemized Deductions for You"
At the bottom of that screen, you can override to standard deduction.
