You'll need to use overrides. On the What-If Worksheet, override the values in columns 2 through 4 of line 32 and enter $7,000 or whatever amount you propose to contribute.
Don't expect 2018 TurboTax to be updated for the 2019 IRA contribution limit. Many of the limits that change from 2018 to 2019 may not even be corrected in the initial release of 2019 TurboTax if past history of TurboTax is any indicator.
Entries on the 2018 IRA Contribution Worksheet are subject to 2018 limits. If you are trying to simulate an entire 2019 tax return, not using columns 2 through 4 of the What-If Worksheet, to adjust the IRA contribution limit you'll need to override lines 3 and 4 of the IRA Deduction Worksheet. You might also need to apply overrides to other limits such as the MAGI limits for determining deductibility of your IRA contribution, reduce your birth year by one, etc. You'll also need to do your own tax calculation since the only place that TurboTax can use 2019 tax brackets is in columns 2 though 4 of the What-If Worksheet. If you do enough overrides, though, you can generally get a pretty accurate simulation of an entire 2019 tax return.
The What-If Worksheet is incapable of determining the amount of any possible Retirement Savings Contributions Credit. You'll have to simply adjust the amount on line 51 columns 2 through 4 based on the amount of credit you determine yourself.
