accidently turned on magnifier. Cannot do anything on screen on iphone

Try double tapping the screen with 3 fingers.

Try to use Siri to “turn off zoom”

If you have set up the shortcut you may be able to triple-tap using two fingers to Zoom out.

Else: Apple support's article (link below) tells how to use Magnifier:\

Eg: Freeze the frame

1. Tap the Freeze Frame button .
2. Use the controls to zoom and adjust the image.
3. When you finish making adjustments:

• • To save the image to your Photos library, tap the Share button  and tap Save Image.
  • To freeze another frame, tap the Multi-Photo Mode button .
  • To return to the live lens, tap the End button .

Use Magnifier on your iPhone or iPad - Apple Support