This is for a Federal Qualified Disaster Loss. The instructions for the form request this statement. I find a Form 4684 "Smart Worksheet" in the print out of the TurboTax worksheets, but not a way to add a statement for the IRS
In order to do this, you would need to print and file your return by mail. Write "RP 2018-08" at the top of Form 4684 and attach the required statement.
From the Instructions for Form 4684:
If you use one of the safe harbor methods provided in Revenue Procedure 2018-08, you must attach a statement to Form 4684 stating that you used Revenue Procedure 2018-08 to determine the amount of your casualty loss. Include the specific safe harbor method used. When completing Form 4684, do not enter an amount on line 5 or line 6 for each property. Instead, enter the decrease in the FMV determined in the relevant safe harbor method on line 7.