How do I install CarPlay on iPhone SE 2020

You don't "install CarPlay".

It's built into iOS.

Does the head unit in your car support CarPlay?

Press and hold the voice command button on your steering wheel if your car supports wireless CarPlay. Alternatively, make sure that Bluetooth or wireless pairing is enabled on your car. On your iPhone, go to Settings > General > CarPlay > Available Cars and select your vehicle.

OK... so what's the problem? We are not psychic.