Contact or Account Owner

I am trying to mass change the Contact Owner in Sugar Market.  I imported a distribution list into SM and it made me the Owner.  I am trying to update the owner in SM so that it matches the Assigned to person in Sugar CRM.  What is the field name for the Owner Name so that I can upload and overwrite?  See image where Owner Name shows Bradley Weedon.  

See image where Assigned To shows Matt Sims.

The Owner or Assigned To person should be Matt Sims.

This is an issue because I am trying to send emails to customers and I want the actual owner to get the reply emails.

  

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