It depends. Did you make a profit or were the items sold for less than you bought them for?
If you sold these items at a loss, which is most common for selling personal items, and you did not receive a tax reporting form, you can simply leave this information off of your tax return as the personal loss is not deductible.
If you sold the items at a gain, you'll need to navigate to the Income section, choose Investments and Savings, and select Stocks, Cryptocurrency, Mutual Funds, Bonds, Other. Select (+)Add investments, and Enter a different way, then type it in myself and continue. Choose "Other" as the investment type. Complete the interview to enter information regarding the sale, including proceeds and cost basis that will figure your taxable gain.