How to teach GPT using raw data

I have raw data from conversations with my clients, amounting to about 2,5M symbols in TXT format. How can I get GPT to analyze these conversations once and for all, so that it can then answer my questions and provide appropriate responses based on the summarized information from the data? When I try to input the file into the Assistant configurator, it struggles to analyze it and seems like it crashes every time I ask it to summarize the data.