In 2022, the standard deduction was $25,900 for married couples filing jointly, $12,950 for single taxpayers and married individuals filing separately, $19,400 for heads of households.
To deduct gambling losses against winnings, you must list all your itemized deductions, including the gambling. Itemized deductions include unreimbursed medical expenses (over a certain threshold), mortgage interest, state and local taxes, gifts to charity, and gambling losses. If, after listing all those items, they are still less than the standard deduction, you will use the standard deduction and get no extra benefit from anything you list, including gambling. Or, suppose your other itemized deductions are $10,000, and you have $10,000 of sports betting losses. Because $20,000 is more than the standard deduction of $12,950, you will use the itemized deductions, but the extra benefit of listing the gambling is $7,050, not $10,000.
If you are using Turbotax, you can prepare an amended return and you should list all the itemized deductions (there is an interview and it will ask about everything so you don't miss anything.)
Or, if the IRS only wants to see a schedule A because they have the rest of your details and just want to know what you want to claim, you can download the schedule A and the instructions here.
https://www.irs.gov/pub/irs-prior/i1040gi--2022.pdf
https://www.irs.gov/pub/irs-prior/f1040sa--2022.pdf
