Getting error M7021 "Deficit of PU GR" because Return amount is 20,000 and GR amount was 17,000 how can I fix it?

There was a mistake making material movements but when I try to fix it I get error M7021, when I check the amount in the return document is bigger than what the Goods receipt was, where should I look to fix this?

Thank you very much and Regards,

Carlos