Get one of the better llama versions fine-tuned on code (e.g. WizardCoder), take your entire code base and create embeddings from it, put those into a vector database.

Now, every time you ask your LLM a question about your code base, you first turn that prompt into an embedding and perform a search on your vector database. The results of that search are appended as context to the actual prompt before passing it to the LLM itself.

There's tons of packages that help with all of that, Langchain and Faiss are probably the most popular right now.