Rashi on Numbers 5:7/רש"י על במדבר ה׳:ז׳

1את 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).

2לאשר 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).