Unless the plan calculated the taxable amount in box 2a then you would use the "general rule" for a non-qualified annuity with a after-tax basis if box 2a is blank and box 2b (not determined) is checked. You do not change the box 7 codes.
See IRS Pub 939.
https://www.irs.gov/pub/irs-pdf/p939.pdf
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
