All perfect praise be to Allah, the Lord of the Worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.
The Prophet, sallallaahu ‘alayhi wa sallam, said: "(The performance of) ‘Umrah is an expiation for the sins committed in the interval between it and the previous ‘Umrah; and the reward of Hajj mabroor (an accepted Hajj) is nothing but Paradise." [At-Tirmithi: hasan saheeh]
The author of Tuhfat Al-Ahwathi, said, in interpretation of the hadith reported by At-Tirmithi “The hadith means that ‘Umrah serves as expiation for the minor sins that were committed in the interval between it and the previous one.”
Imam An-Nawawi wrote in the explanation of Sharh Muslim:
The hadith underlines the excellence of performing ‘Umrah and highlights that it is an expiation for the sins that were committed in the interval between it and the previous one. This is only for minor sin—not for major ones—because major sins, as Al-Qaadhi said, are expiated by repentance or by the mercy and grace of Allah, the Exalted. This is the adopted view of Ahlus-Sunnah Wal-Jamaa‘ah.
Allah Knows best.