I receive a CSA 1099R. On it, there is a Box 7. (Distribution Code(s)) where it says "2 - NONDISABILITY".TurboTax wants info for a box 7a AND a box 7b. What do I do?

Is it necessary for me to make entries for TurboTax's Box 7a AND Box 7b. Since my form CSA 1099R only has a Box 7 - not divided into a and b - what do I enter and where do I enter it?