I owned rental property that I sold in 2019 but still had some costs paid for it in 2020. how do I file those?

You can deduct those expenses on the final schedule E for rental income and expenses you prepared in 2019, or if they applied to the sale of the property, you can enter them on the sales entry in 2019. You will have to amend your tax return for 2019 to make the changes though.