Hi Tony,
Can you confirm if you are referring to the Team and Person entities that are shipped with CDS, or just using that as an example? I'll try and answer for both just in case.
For the Team and Person that exist within the model that comes with CDS, there is a third entity that maintains a many-to-many relationship for Team and Person (a Team can have many people, and a person can be a part of many teams). This entity is called "Team member" and if you wish to remove a relationship between a Team and Person, you would delete the record in "Team member" that connected the two.
For your more generic example, where Entity A has a lookup field to Entity B and you want to remove the relationship of a specific record - you should be able to simply clear the value from the field in Entity A (unless you have made it required) which would remove the relationship on the specific record, but not the entities themselves.
Let me know if I've misunderstood.
Thanks