I am a retired Federal employee. When I enter my 1099R data, I am not offered an opportunity to indicate I am entering data from a CSA 1099-R. How do I indicate this??

Enter a 1099-R  here:

Look again ... delete the one you have and choose the correct form ...

Federal Taxes,
Wages & Income
(I'll choose what I work on - if that screen comes up)
Retirement Plans & Social Security,
IRA, 401(k), Pension Plan Withdrawals (1099-R).

OR  Use the "Tools" menu  (if online version left side) and then "Search Topics" for "1099-R" which will take you to the same place.

Be sure to choose which spouse the 1099-R is for if this is a joint tax return.
Be sure to pick the correct 1099-R type:  Standard 1099-R, CSA-1099-R, CSF-1099-R, RRB-1099-R.