How do I remove segments from a subscriber?

You cannot remove segments from individual subscribers in the same way as the permission with tags.

The reason is that segments are based on rules that are based on subscriber data for each customer. Segments are created based on rules controlled by customer behavior and their subscriber data. See the example below where the filter is controlled by completed purchase (OrderCreated) of a dress, which means that the customer gets the filter "Dresses".

To adjust subscriber data, correct the customer's information from the ground up in your database.