Set up the TNS Service Names:
- tnsnames.ora:

 ORACLE12.1_HOST_NAME_ORA =
   (DESCRIPTION =
     (ADDRESS_LIST =
       (ADDRESS = (PROTOCOL = TCP)(HOST = host_name)(PORT = 1521))
     )
     (CONNECT_DATA =
       (SERVICE_NAME = service_name)
     )
   )

Set up the ODBC connections:
- odbcinst.ini:

 [OracleODBC-19g]
 Description=Oracle ODBC driver for Oracle 19g
 Driver=/usr/lib/oracle/19.19/client64/lib/libsqora.so.19.1
 Setup=
 FileUsage=1
 CPTimeout=
 CPReuse=
 DriverLogging=7
 
 [OracleODBC-11]
 Description=Oracle ODBC driver for Oracle 11
 Driver=/home/bob/ODBC_drivers/Oracle/11/instantclient-odbc-linux.x64-11.2.0.4.0/instantclient_11_2/libsqora.so.11.1
 Setup=
 FileUsage=1
 CPTimeout=
 CPReuse=
 DriverLogging=7

- odbc.ini:

 [ORACLE12.1_VMDBSRV015_ORA]
 Driver = OracleODBC-19g
 ServerName = ORACLE12.1_HOST_NAME_ORA
 #Description = Oracle 12.1 BT connection
 UserID = USER_NAME
 Password = PWD

Test the connection:

 isql -v ORACLE12.1_HOST_NAME_ORA USER_NAME PWD

If you have any questions or encounter any difficulties, please contact us at support@ispirer.com