After the Jet instance has been authorized, fields can be mapped by going to Settings > Plugins > Jet then clicking Custom Field Mappings:

The following modal will pop up and allow for Universal Product Fields and Attribute Fields:

These fields can be mapped to default fields added to the account (i.e. size, color, etc) or custom user fields added in Settings > Custom Fields. Fields can be filtered for each tab by using the Filter text field: 

The above screenshot is a search for fields with 'audio' contained under the Attribute Fields tab. In order to search within the Attributes Fields, the tab needs to be selected first before entering the search string.

Once all desired fields are mapped, the "Save" button can be clicked to save changes: