1. Edit job and set empty schedule.
You must look at the url and remember id!
2. You should open tab "Settings" , open "jobs" , click "Generate new key" and click "Save".
You should open tab "Settings" , open "jobs" (again!) and copy key only
3. Modify this url .
http://{site.com}/wp-admin/admin-ajax.php?action=order_exporter_run&method=run_one_scheduled_job&schedule={job_id}&key={key}
{site.com} is your website url
{job_id} - you get this ID at step #1
{key} - you get this key at step #3
if you use HTTPS, replace http with https too!
Final result must looks like
4. Test it, open this url in browser , you should get message
Scheduled job #XXX. Result: .....
You can use this url in external scripts OR call it (for example) via curl/wget