Default Sales Person to No Sales Credit when submit changes for new service activity created

 Good Afternoon, How do you default Sales Person to No Sales Credit on sales order for a newly create service activity?
I created a new service activity and a new order type. When i create Service request using this service activity and submit charges the sales rep on the sales order is blank.
I would like the sales rep to default to no sales credit.
I have add the new order type to existing defaulting rules but still the sales rep is left blank.

Any help is greatly appreciated.

Thank you,

Angela