This is very clear and helpful. I made the same mistake and inadvertently made a 2nd $6K contribution to my ROTH IRA in July 2021 which did not get detected since I had switched brokers earlier in the year and failed to recall the earlier $6K contribution. The error was made in my ROTH IRA at Fidelity and they actually have a form for this error which they'll process to generate the 1099-R. I have yet to get this form back from them (I only recently detected the mistake while working on my return for 2021 .. so have yet to file). Based on my reading of the relevant IRS documents, and from discussion with Fidelity, my IRA trustee will remove the excess $6K plus any earnings in the IRA between the point I made the excess and contribution and its removal which can be attributed to this $6K (so, pro-rated based on the total IRA balance between these two time points). Then these earnings will need to be included as income for 2021 and, lastly, since I'm under 59 1/2 , I will also be assessed a 10% early withdrawal penalty on these earnings. The $6K excess gets removed without being treated as an early distribution. I'll update this comment once I get the 1099-R from Fidelity. The form at Fidelity is "IRA Return of Excess Contribution Request".
