To take the Retired Public Safety Offer deduction for up to $3,000 you will need to reduce the amount in box 2a of the applicable 1099-R by the amount of the deduction. Once you have continued out of the 1099-R, you can go to Nontaxable Distributions and check the box for the PSO exclusion.
Currently, if you need to use the simplified method worksheet, you will complete the worksheet to get the number for box 2a. If you click continue, it will carry that number to box 2a for you but will not allow you to edit. You will need to delete the worksheet once you have the number and go back and enter the number minus the deduction amount up to $3,000.