I have a small database of about 300 `contacts` and my company is looking to implement a new mapping system to assign each `contact` to a sales rep. 

After I have exported the data, cleaned up any duplicates, and assigned each a sales rep based on our new system how do I load the records back into production using the sandbox in order to update the contact owner field with the changes for all of the records at one time? 

Thanks for the help!