You don't checkmark something they didn't mark. You are not the originator of that info. Just enter what you see.
If you need help, Google this:
irs 1040 1099-r simplified method worksheet
That worksheet is in the Form 1040 instructions.
"Level Up" is a gaming function, not a real life function.
So he retired at 58 and would have recovered his cost in 260 months -- by 2016. Usually, though, when I see a blank for "taxable amount," there is some special situation, like disability retirement or a survivor pension. Helps to know when he started his federal career, to figure how much he would have paid in after-tax contributions.
Rule of thumb: If he has a pension file dating back to when he retired, take a look. Otherwise, it's all taxable. And Pub 721 is a good source.
Start at page 8 and estimate if they have recovered their contribution. https://www.irs.gov/pub/irs-prior/p575--1994.pdf
Once you determine, you should be able to input the computed amounts into the system so it would automatic. I don't do PS, so I can't help with those steps. Come back if you need help and I will try to get someone to do so.