See if the following can work for you:
You should be able to mirror the display of your iPhone's rear camera onto your iPad using a feature called "Continuity Camera" or by connecting them with cords. Here are two methods you can try:
Method 1: Continuity Camera (Wireless)
- Make sure both your iPhone and iPad are connected to the same Wi-Fi network and are running on iOS 12 or later.
- On your iPad, swipe down from the top-right corner to open the Control Center.
- Look for the "Screen Mirroring" or "AirPlay" icon (it looks like a rectangle with an arrow pointing upwards) and tap on it.
- In the list of available devices, you should see your iPhone listed. Tap on it to establish the connection.
- Once connected, your iPad's screen will mirror the display of your iPhone's rear camera. Open the Camera app on your iPhone, and you should be able to see the live preview on your iPad.
Method 2: Wired Connection
- Get a Lightning to USB cable (or USB-C to Lightning cable if your iPad has a USB-C port) to connect your iPhone and iPad together.
- Connect one end of the cable to the Lightning port on your iPhone and the other end to the Lightning or USB-C port on your iPad.
- On your iPad, open the "Photos" app.
- Tap on the "Import" tab at the bottom and select your iPhone from the list of available devices.
- Once connected, your iPad will display a live preview of your iPhone's rear camera. You can use the "Record" button in the Photos app to start capturing a video.
Ref: Use Continuity to connect your Mac, iPhone, iPad, and Apple Watch - Apple Support