FHIR to JSON data

Hello to everyone and sorry to bother you with this simple question, so I am not developer but need to know it if possible in simple words…
If I have a few tables and FHIR gets the data from all of them and converts it to JSON format document, what exact service make this convertation?

FHIR is the syntax of the data in the JSON document. It also defines an API for certain types of services. Converting data from a proprietary format into FHIR is not a ‘standard’ service that’s defined in that API, though FHIR does define mechanisms to allow you to define your own custom operations. It would be possible for you to define a custom operation that could consume data from certain tables and expose them as a FHIR resource. However, typically the conversion of data into FHIR is something that’s done using custom software