Not adaptable in different social settings? If I talk to a group of people I can’t talk to them individually. If I talk to someone individually it’s hard for me to talk in a social setting

How do I overcome this? I don’t even know why this happens. If im talking to one person I freeze when another person is added to the convo. When Im talking to a group I freeze when im talking to them individually.

How do I become more adaptable and get the courage to talk in these types of social settings?