If you and your spouse file separate returns and one of you itemizes deductions, the other spouse must also itemize, because in this case, the standard deduction amount is zero for the non-itemizing spouse. You should amend your 2018 return.
Itemized. If you are married, then you have two options. You can file "Married Filing Jointly" or "Married Filing Separately." You cannot both file Single.
Your prior-year tax returns should both be amended for the federal and state returns. It is not allowed for you both to file single when you are married. It will cause you more problems to not fix your prior year's tax return as soon as possible.
The rules are different depending on the filing status. Your best bet is to amend last year's return and with the filing status of "Married Filing Joint."
If you are not sure what filing status to use, try the Interactive Tax Assistant Tool for Filing Status from the IRS.
Filing an amended return in TurboTax is easy. This link explains how to amend whether you are using Online or Desktop. You will have to print it out and mail it in.
I recommend you report any state refund as received, if you live in a state with income tax, on this year's return.
If you both filed single last year and only one of you itemized, then you should answer the question about itemizing with a Yes.
TurboTax is trying to determine if your state tax refund from last year is income this year. This would only be so if you itemized. Make sure that you enter only the refund from the party that itemized. The refund from the spouse that filed with a standard deduction is not taxable.
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