Deductions & credits

You can't. You can't claim more gambling losses than the amount of gambling winnings that you claim. When you claim your gambling winnings, and continue the interview, a few pages later you can enter your gambling losses, but only up to the amount of winnings that you claim.
Gambling losses do NOT offset gambling winnings dollar for dollar. Instead, they are an itemized deduction. Itemized deductions provide no tax benefit until all of them added together are more than your standard deduction.