Code DD is the employer's contribution to your employer sponsored health insurance, it has no effect on your taxes, that number is there for information only.
Qualified workplace plans have several different codes depending on the exact type of plan. A list of codes is here.
https://ttlc.intuit.com/turbotax-support/en-us/help-article/taxation/letter-codes-box-12-w-2-mean/L6...
IRAs are covered by a different section of the tax law than qualified workplace plans, and they have different rules, even though they have a similar purpose.
If you make pre-tax workplace plans, that fact is supposed to be on your W-2. Your box 1 taxable wages are already reduced by the amount of the contribution, and the contribution (along with any employer match) should be reported in box 12. Do not report workplace plans in the section for IRAs. If you think your W-2 is wrong, you need to contact your employer.
