You can use Oracle SQL*Loader to load data from local files in your client machine into Autonomous Transaction Processing.
Using SQL*Loader may be suitable for loading small amounts of data, as the load performance depends on the network bandwidth between your client and Autonomous Transaction Processing. For large amounts of data Oracle recommends loading data from the Cloud Object Storage. (For information on loading from Cloud Object Store, see Load Data Using Oracle Data Pump).
Oracle recommends using the following SQL*Loader parameters for the best load performance:
readsize=100M bindsize=100M direct=N
For detailed information on SQL*Loader parameters see Oracle Database Utilities.
For loading multiple files at the same time you can invoke a separate SQL*Loader session for each file.
Autonomous Transaction Processing gathers optimizer statistics for your tables during bulk load operations if you use the recommended parameters. If you do not use the recommended parameters, then you need to gather optimizer statistics manually as explained in Manage Optimizer Statistics or wait for the automatic statistic gathering task to kick in.
For detailed information on SQL*Loader see, Oracle Database Utilities.