For 2019, see this
https://www.irs.gov/businesses/small-businesses-self-employed/deceased-taxpayers-filing-the-final-re...
and this
https://www.irs.gov/pub/irs-pdf/p559.pdf
You must be the legal administrator of the person's estate under your state law. This may require filing a form, if you have not already done so. You may need to check with an attorney.
If your spouse is due a refund, you will have to include form 1310 with the return to get the refund paid into your name. If you were not the person's legal heir at the time, the refund will have to be paid to the legal heirs. (For example, if the person died unmarried and without a will, state law might require the refund to be paid to the person's children, parents or siblings rather than an unmarried domestic partner.)
