Open the Contacts app or Phone app
Tap Lists or Contacts
Look for the Duplicates Found prompt at the top
Tap View Duplicates
Tap Merge All or select individual duplicates to merge
Confirm the merge
If no duplicate prompt appears, open each duplicate contact manually
Edit one contact and delete the extra duplicate entry
To remove synced duplicates, check iCloud, Gmail, or other account settings
Turn off duplicate contact syncing if needed
Restart your iPhone after making changes