How do I get my 4 digit code

Set up the Apple TV Remote in Control Center

1. Open Control Center:

• • On iPhone X or later or iPad with the latest version of iPadOS: Swipe down from the upper-right corner of the screen.
  • On iPhone 8 or earlier or iOS 11 or earlier: Swipe up from the bottom edge of the screen.

1. Tap the Apple TV Remote.
2. Tap your Apple TV or smart TV from the list.
3. When asked, follow the onscreen instructions to enter a four-digit passcode into your iPhone, iPad, or iPod touch. If you have Apple TV (3rd generation), use your Siri Remote or Apple TV Remote to enter the four-digit passcode into your Apple TV. 

https://support.apple.com/en-us/HT201664

Also, I found out that I have to have my iPhone or iPad within a foot or so of the Apple TV. It never works for me more than 3 feet away.