What must I do after having excommunicated someone who denied a Qur'anic verse, believing it to be "Indeed, Allah does not waste the reward of those who do good deeds," then it later became clear to me that the correct verse is "Indeed, We do not waste the reward of those who do good deeds"?

Do not rush to judge someone as an infidel. Indeed, whoever denies something in the Qur’an, being ignorant of its presence therein, does not become an infidel until proof is established against him. If you confront the person with what was mentioned, seek his forgiveness for the injustice. If you do not confront him, then it is hoped that your seeking forgiveness for him will be sufficient, due to the potential harm that might result from informing him. As for giving charity on behalf of a living person and donating its reward to him, there is a difference of opinion regarding its validity.