How can i update faiss trained index incrementally?

Question

I am using Faiss to index some sentences, and the sentences will add by user erverday, so i need to update index file everyday, i just load the trained index using faiss.read_index(file) and use indexer.add to add the embeddings incrementally, finnaly use write_index to save index file. but it seems not work, Can someone give me some advice?