Here Oliver Cowdery initially wrote “which will atone for another”; then virtually immediately he supralinearly inserted “the sins of ” (there is no change in the level of ink flow). Elsewhere the text consistently uses the verb phraseology “to atone for sins” (seven times), never “to atone for a person”. In fact, there are two other passages that specifically refer to blood as atoning for sins:
Here in Alma 34:11, the critical text will follow the corrected reading in 𝓞.
Summary: Maintain in Alma 34:11 the corrected reading in 𝓞, “his own blood which will atone for the sins of another”.