You won't be able to add your EIN from your Shopify admin, but if you get in touch with our live Support team through the Help Center they'll work with our Payments team to get your information updated. Your SSN will always remain on the account, even if you have an EIN for your business.
While we’re not able to provide account-specific support via the Shopify Community at this time, we’d be happy to continue assisting you through live chat, email, or callback.
Since this is the next step I've marked this reply as the solution for the benefit of others who may discover this topic. Thanks!
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