Dynamically expand record from API repsonse

I have a series of API requests that I have dynamically programmed into a function. However, the response takes the form of a single named record containing a list. How can I expand/select this record programatically without explicitly listed the record's name(i.e: Source[assets], Source[users], Source[locations]), or is there a way that I can write the function such that a parameter is used in a record name reference?