Passing Custom Field values to MailChimp

I created a couple of custom fields at checkout and now I want to move that data over to MailChimp using a workflow created in AutomateWoo. By default, AutomateWoo gives you a lot of variables to select from, like {{ customer.email }} for example. But what about custom fields I create here in Checkout Manager? How can I pass on those fields over to MailChimp?

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