The holdup is the IRS. They have not released the 1040X instructions for tax year 2018.
IRS Form 1040X, Amended U.S. Individual Income Tax Return is estimated to be available on 02/22/19
See this TurboTax support FAQ for IRS forms availability - https://ttlc.intuit.com/questions/1908854-irs-forms-availability-table-for-turbotax-individual-perso...
The tax return should not be amended until the tax refund has been received from the IRS.
See this TurboTax support FAQ for amending a tax return - https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed
