My 2019 1099-R includes an excess contribution withdrawal plus regular withdrawals. The form does not distinguish between them. How do I report the regular withdrawals?

The excess contribution was in 2018, was not deducted, had a small net gain reported as income in 2018, and was withdrawn in January 2019 - which is why it is on the 1099-R for 2019. Even if I call the brokerage that sent the 1099-R to correct it, I don't see how I can prove to them that part of the withdrawals were for an excess contribution. If I don't report the full amount shown on the 1099-R, I am afraid that will trigger an audit. What should I do?

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