Edit a Feed Element

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() WITH USER_MODE ORDER BY CreatedDate DESC];
if (feedItems.isEmpty()) {
    // Return null within anonymous apex.
    return null;
}
String feedElementId = feedItems[0].id;

ConnectApi.FeedEntityIsEditable isEditable = ConnectApi.ChatterFeeds.isFeedElementEditableByMe(communityId, feedElementId);

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

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

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

    feedItemInput.body = messageBodyInput;

    ConnectApi.FeedElement editedFeedElement = ConnectApi.ChatterFeeds.updateFeedElement(communityId, feedElementId, feedItemInput);
}