Edit a Comment

String commentId;
String communityId = Network.getNetworkId();

// Get the last feed item created by the context user.
List<FeedItem> feedItems = [SELECT Id FROM FeedItem WHERE CreatedById = :UserInfo.getUserId() ORDER BY CreatedDate DESC];
if (feedItems.isEmpty()) {
    // Return null within anonymous apex.
    return null;
}
String feedElementId = feedItems[0].id;

ConnectApi.CommentPage commentPage = ConnectApi.ChatterFeeds.getCommentsForFeedElement(communityId, feedElementId);
if (commentPage.items.isEmpty()) {
    // Return null within anonymous apex.
    return null;
}
commentId = commentPage.items[0].id;

ConnectApi.FeedEntityIsEditable isEditable = ConnectApi.ChatterFeeds.isCommentEditableByMe(communityId, commentId);

if (isEditable.isEditableByMe == true){
    ConnectApi.CommentInput commentInput = new ConnectApi.CommentInput();
    ConnectApi.MessageBodyInput messageBodyInput = new ConnectApi.MessageBodyInput();
    ConnectApi.TextSegmentInput textSegmentInput = new ConnectApi.TextSegmentInput();

    messageBodyInput.messageSegments = new List<ConnectApi.MessageSegmentInput>();

    textSegmentInput.text = 'This is my edited comment.';
    messageBodyInput.messageSegments.add(textSegmentInput);

    commentInput.body = messageBodyInput;

    ConnectApi.Comment editedComment = ConnectApi.ChatterFeeds.updateComment(communityId, commentId, commentInput);
}