Check for duplicate emails in new sign up list?

I have an existing Convertkit email list (A) and am also starting a brand new Convertkit account (B) for an annual event collaboration. I want to be able to tag subscribers who end up on both of my Convertkit email lists so that I don’t over-send emails to them.

Ideally, when someone subscribes through the new Convertkit (B), I’d like to…

  1. check if their email address already exists on my original account (A)
    If so, I’d then like to…
  2. add a tag to the subscriber in both A and B Convertkit accounts.

Steps taken so far

I have connected my two Convertkit accounts in Make with the API secret. I looked into logical conjunction and I think I might need a get() or map()function to start?

I’m getting closer, but still confused about how to approach this in a Make scenario. Advice is welcome. Thanks.

Can anyone help with this?