In most cases NG handles data updates itself. However, depending on the definition of the update process, the import will not be initiated by NG itself, but via the Import interface. This makes sense especially if the data is provided using the Push method.
If a URL from which your export data can be drawn is stored in the FactFinder Search configuration, it is possible to download this before the import, so that it can be loaded.
REST-Interface
The technical documentation of the REST-API is contained in the search application itself and can be accessed via [your NG server]/fact-finder/swagger-ui.html . It can be also accessed via the following URL:
Swagger Link
Methods are documented under records. In addition to viewing the parameter documentation, you can also test a query and view the results. The documentation was created with Swagger, so you can use Swagger Codegen to generate a client to use in your code.