Retrain for what exactly? If driverless trucks and cars eliminate a several million truck drivers and taxi cab drivers where do we find jobs to replace those l

Retrain for what exactly? If driverless trucks and cars eliminate a several million truck drivers and taxi cab drivers where do we find jobs to replace those lost occupations? We have millions of underemployed people already, working 30 hours a week at Walmart and similar jobs. It's not like there are millions of jobs just looking for trained people to fill them.