Welcome to the community @harry.fremantle 

To do this, you import a csv of those contacts into your target Klaviyo list. As they are already in Klaviyo, that import could just be email addresses.

Set the target Klaviyo list to single opt-in before import. If you want double-opt in, you can always flip it back after importing. 

During the import of your csv to the Klaviyo list make sure you check the control ‘Yes, update subscription status for all imported contacts to 'subscribed'’. After the import, those contacts will be set to ‘email subscribed’.

I suggest you do a trial run with test contacts + a test list to ensure you’re comfortable with the process before you do the actual list.

Hope that helps

Andy

Thanks @bluesnapper! Really useful 

No problem @harry.fremantle !

Regards

Andy

Adding a quick note here, when you do import make sure there's no (welcome) flow that gets triggered

Omar Lovert // Polaris Growth // Klaviyo Master Platinum Partner

We help with e-commerce growth through CRO, Klaviyo and CVO