I just received a w2c where they forgot to add DD contributions in box 12

If that is all that changed on your W-2 there is no reason to amend for the cost of employer-sponsored health overage. The amount reported with code DD is not taxable.

Do not amend your tax return. Code DD in W-2 box 12 is just for your information. It is not actually entered on your tax return, and it does not affect your tax return in any way. An amended return would not show any change.