Yeah, basically you have three options:

1. Create and train your own LLM. This is hard and needs a huge amount of training data, hardware,…
2. Use one of the available models, e.g. GPT-4. Give it a special prompt with instructions and a pile of data to get fine tuned with. That’s way easier, but you need good training data and still a medium to hard task.
3. Do variant 2, but don’t fine-tune the model and just provide a system prompt.