Assigning order number

Good afternoon! Is it possible to assign the order number?

In order to assist you better, please provide us more details to your problem. 

I'm just assuming you want to use the Unique ID field to generate serial numbers on the form. Please check this guide: https://www.jotform.com/help/79-How-to-Add-Custom-Unique-IDs-to-your-Form-Submissions

Hope that helps.