How to purge the log entries for a specific dbms_scheduler job

exec dbms_scheduler.purge_log(log_history=>0, job_name=>'YOUR_JOB_NAME');

Zero is actually default for log_history, it doesn't have to be specified.

If you want to save some of the logs, you can specify for example that Oracle should only purge logs older than, say, two days:

exec dbms_scheduler.purge_log(log_history=>2, job_name=>'YOUR_JOB_NAME');