Whatever you heard is wrong or misunderstood.
You obviously made contributions at some point in the past to open the Roth IRA. Roth IRA withdrawals are always in the order of contributions first, conversions second, and earnings last. Withdrawal of contributions is always tax-free. Withdrawal of conversions is tax-free if it is more than 5 years since the conversion was made. Withdrawal of earnings is subject to income tax plus the early withdrawal penalty if you are under age 59-1/2.
When you enter the 1099-R, turbotax should ask you for your total lifetime contributions to the Roth IRA, any conversions and their dates, and the total of any prior withdrawals. Then it will calculate the taxable amount. For example, if you opened the Roth IRA with a $5000 deposit and never contributed more, and never withdrew before, then the first $5000 you withdraw is tax-free and the rest is earnings subject to tax plus penalty.
If you don't know the amount of prior contributions, ask the broker. You need to keep track, the IRS does not keep track for you.
