I converted $12000 to backdoor Roth for previous year before April

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I converted a total of $12000 to backdoor  in 2022 before April. Of which $6000 was for the previous year 2021. What do I enter here $6000 or $12000? My tax refund decreases when I enter $6000 but corrects when I enter $12000, however  it says I owe a penalty because $6000 is being considered as an excess, although it was my contribution for the previous year.