Where do I enter my gambling losses! I already entered the winnings.

After you have entered your gambling winnings, click Done on the page titled Here's your W-2G info. Two screens later, you will arrive at the screen shown in the attached screenshot where you can enter your winning losses.

https://www.irs.gov/help/ita/how-do-i-claim-my-gambling-winnings-and-or-losses

Losses are an itemized deduction.  If you do not have enough itemized deductions to exceed your standard deduction, your losses will have no effect.

https://blog.turbotax.intuit.com/income-and-investments/how-are-gambling-winnings-taxed-8891/

https://ttlc.intuit.com/questions/1900352-can-i-deduct-my-gambling-losses

2018 Standard Deductions:

Single   $12,000  (+ $1600 65 or older)

Married Filing Separately    $12,000  (+ $1300 65 or older)

Married Filing Jointly  $24,000  (+ $1300 each spouse 65 or older)

Head of Household  $18,000  (+ $1600 65 or older)