A korban chatas, korban asham, death, or Yom Kippur provides atonement together with doing teshuva.

Teshuva helps for positive or negative commandments. On greater prohibitions teshuva helps in that it suspends the punishment until Yom Kippur which then provides the atonement.

Yuma 8:9

If someone says, ‘I will do a prohibition and then do teshuva’, Hashem will not help him do teshuva.

If someone says, ‘I will do a prohibition and Yom Kippur will atone’, Yom Kippur will not atone.

Sins between man and Hashem, Yom Kippur will atone. Sins between man and his fellow man, Yom Kippur will not atone.

R’ Akiva says, ‘ Yisrael, you are praised for who cleanses you, Hashem. Just as a mikveh makes people tahor so Hashem purifies Yisrael.’