This article in ShippingEasy's knowledge base explains the steps to take to export your products to a CSV file.
The CSV you export can be mapped and imported into GroovePacker directly but there are a couple of differences worth noting that call for special attention.
Kits
GroovePacker uses a separate file to import kit data. ShippingEasy includes the kit data in the products data csv. This means that kits will not be recognized properly in the csv exported form ShippingEasy.
The workaround is to leave the kit SKUs out of the product export and create an mock order in ShippingEasy that contains all of your kits. When you import this mock order into GroovePacker it will create the kits automatically.
Alias SKUs
GroovePacker uses a separate column in the product csv to import each additional alias. ShippingEasy includes all aliases in the same cell and separates them with the pipe | character. This means that aliases will not be recognized properly in the csv exported from ShippingEasy.
The workaround is to leave the SKUs that have aliases out of the product export and create a mock order in ShippingEasy that contains all of your SKUs that have aliases. When you import this mock order into GroovePacker it will create these skus and all of their aliases will be added automatically.