You enter it under the retirement income section for 1099-Rs. When you first add it though, you have to choose what kind of 1099-R it is. This one is the fourth selection down. If your fields don't match up you probably didn't choose the right type. If you chose the social security topic, that's the RRB-1099 with no -r at the end.
You can go to Federal Taxes, Wages and Income, Choose what I work on if you see it. If not, just scroll down to the Retirement Income section. Update the social security topic if that's where you entered it, and you should be able to delete the form. Update the pension topic and you'll see a little table of what you entered. Edit this one and make sure you chose the right type
