Can I amend a return from 2019 using Turbo Taxif I filed online with H&R Block?

CAN I USE TURBOTAX TO AMEND IF THE RETURN WAS PREPARED SOMEWHERE ELSE?

If you did not use TurboTax to prepare your tax return, it is possible to amend the return using TurboTax but it will really be a pain.  It would be better to use the software or service used to file originally.  If a paid preparer made a mistake on your tax return, that tax preparer should do the amended return for you at no charge.

In order to use TurboTax to amend your return, you need to purchase the desktop software for the tax year and re-create the return EXACTLY as it appeared when it was filed with the IRS/states.  Every line has to be the same.  Then you have to "trick" the software into thinking you filed by saying you will mail the return. (but do not mail it)   AFTER that, you use the software to prepare a Form 1040X, which has to be printed, signed and mailed to the IRS.  It takes the IRS about 6-12 months to process an amended return

"Someone told if I lost as much as I won I didn't need to include."

That was very poor information.   You are supposed to include all of the gambling winnings.   Losses might not have any effect on your tax due or refund, unless you had enough itemized deductions to exceed your standard deduction.   Otherwise, only the winnings count as income and the losses do nothing to affect your results.

Gambling winnings are taxable income.  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

Did you itemize deductions when you filed your 2019 return?

2019 Standard Deduction Amounts

Single $12,200   (+ $1650 65 or older)

Married Filing Separate  $12,200   (+ $1300 if 65 or older)

Married Filing Jointly $24,400   (+ $1300 for each spouse 65 or older)

Head of Household $18,350  (+ $1650 for 65 or older)