פּירוש אויף במדבר 5:7

את אשמו בראשו [HE SHALL RESTORE] THAT WHEREIN HE IS GUILTY, AS BEING THE CHIEF SUM — This means, he shall restore the principal about which he has sworn falsely (Bava Kamma 110a).

והשיב את אשמו, and he shall make restitution for his guilt, etc. The Torah again switched to use of the singular although the verse had commenced by speaking about sinners in the plural confessing their guilt. The reason is that when it comes to having to confess one's guilt all sinners are in a similar situation. When it comes to making restitution, however, this is not so as the Torah makes allowances for poor people whose sin-offering consists of lower priced birds or even a meal-offering only. We have learned this in Leviticus 5,7-5,13.

והשיב את אשמו, the capital value minus the penalty.

לאשר אשם לו [AND HE SHALL RESTORE THE PRINCIPAL … AND GIVE UNTO HIM] TO WHOM HE IS GUILTY — i.e. unto him to whom he (the claimant) owes money (Ketubot 19a).