How do I update custom fields for a contact via the API using the List Management API

How do I update custom fields for a contact via the API using the List Management API

I have added a new contact via API, which is just the email address. I now need to add first name, last name, and a few other custom fields (and their associated data).

I can't seem to find an API that allows me to update contact information?

    Nederlandse Hulpbronnen