You should receive a 1099-R form for distributions from retirement accounts. If you did not receive the forms 1099-R, contact the custodian.
If you received the forms, but forgot to include them on your tax return, then you will need to amend your return to include them.
But wait until the return is fully processed and you have received a refund/or paid the taxes due for the original tax return.
https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed
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