You can set Omnivore up to use any of the stores. 

Choose which store you want to use and put the ID into Omnivore. 

  • Go to "settings --> feeds". 
  • In the fields Magento Website ID and Magento Store ID, enter the ID you have in Magento. 

See screenshot below to find the ID in Magento. The number showing in the hover text is the ID.