Roth IRA Contribution

I'm filing my 2023 return using TurboTax. It asks me to enter "Prior Year Roth IRA Contributions" (Confirm your net regular contributions prior to 2023 that remain in your Roth IRA). 

So I have contributed $18,000 since 2020.  ($6000 in each year of 2020, 2021, and 2022).  I didn't contribute anything in 2023 but had a $3000 distribution, which I used to pay the downpayment of my first home. 

I'm not sure what number I should put there.  Should I enter $18,000 or $15,000?

And I don't understand why the number I put there makes a big difference on my return. 

I tried to have people at H&R block to do my tax. According to them, I shouldn't put any numbers in the IRA contributions section, as I didn't contribute anything in 2023.  They also said if I want to report prior year contributions, I will have to file an amended tax return.  

Please advise, 

 

Thanks in advance