Hi how can I transfer the movie from iPhone 12 to my big TV screen?

All the ways to watch from the Apple TV app - Apple Support

Apple TV app-supported TVs and third party streaming devices - Apple Support

• Some TVs can have the Apple TV app natively among their smart apps.
• Some TVs are AirPlay-enabled.
• Other TVs will need a HDMI-connected steaming device to have the Apple TV app. This can be an Apple TV box, a Roku, or a Fire TV.

For streaming from your iPhone to the TV, you will need an AirPlay receiving device. This can be an AirPlay-enabled TV, an HDMI connected Apple TV box, or soon a compatible Roku.