The resolution of the story is when Doodle dies and his brother blames himself.
From the beginning, the narrator is embarrassed and ashamed of his little brother. Doodle is expected to die as a baby, and grows up with mental and physical impairments. The narrator often complains about his little brother and sometimes treats him cruelly.
When the narrator tries to teach his little brother to run, disaster results. Like the scarlet ibis that fell from the tree and foreshadowed his death, Doodle has collapsed unexpectedly.
"Doodle!" I screamed above the pounding storm and threw my body to the earth above his. For a long time, it seemed forever, I lay there crying, sheltering my fallen scarlet ibis.
This event resolves the conflict of the narrator being ashamed of Doodle. His conflict is with Doodle, but also with himself. He feels badly for the way he treats his brother. After he dies, he regrets it even more.