Use DBMS_CLOUD_ADMIN.CREATE_DATABASE_LINK to create database links from an Autonomous Database to an Oracle Database Gateway to access Non-Oracle databases.

• Prerequisites to Create Database Links to Non-Oracle Databases with Customer-Managed Heterogeneous Connectivity
  Use DBMS_CLOUD_ADMIN.CREATE_DATABASE_LINK to create database links from an Autonomous Database to an Oracle Database Gateway to access Non-Oracle databases.
• Create Database Links with Customer-Managed Heterogeneous Connectivity to Publicly Accessible Non-Oracle Databases
  Use DBMS_CLOUD_ADMIN.CREATE_DATABASE_LINK to create database links from an Autonomous Database instance on a public endpoint to an Oracle Database Gateway to access Non-Oracle databases.
• Create Database Links with Customer-Managed Heterogeneous Connectivity to Non-Oracle Databases on a Private Endpoint
  You can create database links from an Autonomous Database to an Oracle Database Gateway to access Non-Oracle databases that are on a private endpoint.