You’ll have to retrieve the data in batches. You can use https://kc.humanitarianresponse.info/api/v1/data/XXXX?format=csv&sort={"_id":1}&start=30000 to skip the first 30,000 submissions, for example. The sort part is important; without it, your submissions may not be returned in a consistent order, and the batches may omit or duplicate submissions.
You may also use MongoDB query operators to filter your data, as described in “Query submitted data of a specific form” in the documentation at the top of https://kc.humanitarianresponse.info/api/v1/data.
