As the car owner, you'll receive a PIN code from Volvo support to verify authorisation for certain connected services. This does not apply to cars with Google built-in.
When changing ownership of a car with connected services, there are some steps that need to be taken by both the previous and new owner.
If the previous owner of your car has not removed their profiles and connected phones, a factory reset of the car is needed. You can do this yourself via the car's centre display or ask the previous owner to do it via the Volvo Cars/Volvo EX30 app.