Yes you can change a manual car to an automatic with the proper transmission to engine adapters for the bell housing etc.
Then you just change out the shift lever in the car to the automatic shift lever either on the floor or on the steering wheel.
You may need to change out the steering wheel assembly if you have the automatic transmission shift lever on the steering wheel column.
But usually the transmission shift lever would be on the floor where you would have the manual transmission shifter.
So changing out a manual transmission in a car that is automatic can be done but sometimes the cost may not be worth it.
Unless you love the car or it's an antique car then it may be worth it to change the manual car transmission to an automatic transmission.