ok, so he is limited to contributing $6k p.a. to an IRA. And he did 2x $6k = $12k. 

So how do I treat the 2nd 1099 for $6k.

Everything I am reading says he has to withdraw the "excess" $6k before 4/15 to not incur a 6% penalty.

But will the plan administrator will only generate a 1099 showing the withdrawal from the Roth next year, as a 2021 action.

The question remains how do I treat the 2nd 1099 in his tax return for 2020?