Check you lasttran table. Cannot remember if your version stated above contains the Job last transaction field.
That's where you would (carefully) update it (if available to you).
If not, a better way would be to write a custom trigger upon creation of new jobs to sequence them with alpha and numeric characters - not just numerics.
The issue is with resetting the last Job # would be that you "run into" and existing job number again somehow.
That would most likely crash the DB.