how to delete old sagemaker training/processing jobs ?

Hello.

Jobs cannot be deleted as described in the documentation below.
I think it's safe to ignore it as there will be no charge even if there are still jobs left.
https://docs.aws.amazon.com/sagemaker/latest/dg/ex1-cleanup.html

Training jobs and logs cannot be deleted and are retained indefinitely.

There were some issues on GitHub about deleting jobs, so it may be possible to delete them in the future.
As of March 2024, it cannot be deleted.
https://github.com/aws/amazon-sagemaker-examples/issues/1535