Hi,
If you see the "Remove from collection" option is not grayed out, it indicates that the client is added by direct rule, so we can remove it from collection.
Then add it to collection B use direct rule, right click collection B and select Membership Rules tab, click Add Rule > Direct Rule > next > type a "%" for value and click next > choose Server01 and next > close rule wizard and apply it.
Regards,
Allen