Choosing a good design pattern for processing a large hash field map

So here's the situation. I receive an object through REST controller which contains an instance field that's a hash map, which itself contains lots of fields (70+). Those represent fields on a real life form. Since I have to process data from each of them, how should I organize my code? I inherited this project and the dev before me put it all in a huuuuge method where he parsed every field with if/else. Is there a better approach to this situation?