Open the Compass app
Move the iPhone in a figure-eight motion
Keep moving until calibration completes
Enable Location Services for Compass if needed
Turn on Calibrate Compass in Settings if available
Go to Settings
Tap Privacy & Security
Tap Location Services
Tap Compass
Set access to While Using the App or Always
Make sure Precise Location is on
Restart the iPhone if the compass still seems inaccurate
Remove magnetic cases or accessories if needed
Move away from metal objects and magnets
Recalibrate in a different location if necessary