Hello @JaimeW59 ,
There's a couple different processes you can go through to achieve what you're wanting.
If you don't care about the big list maintaining all the contacts it currently has, then you can go to the 'already registered' and select-all the contacts. From there you can go to Actions > Remove from list > then select the big list. You'll now have the registered list and a smaller "big list."
If you wish to maintain the big list, and instead create a separate, unique 'big list minus already registered,' then the process is pretty similar. Go to your big list, select-all the contacts, go to Actions > Add to list > Create list > then Add the contacts after making the new list. Then it's the same process as mentioned above, go to your registered list, select-all, Actions, and remove those contacts from the new list.
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