Open the Contacts app or the Phone app
Tap Contacts
Tap Lists in the top-left corner if shown
Tap All Contacts
Look for the Duplicates Found card at the top
Tap View Duplicates
Review the duplicate contacts
Tap Merge All to combine all duplicates
Or tap individual contacts and choose Merge
Confirm the merge if prompted
If no Duplicates Found card appears, manually merge contacts by opening one contact
Tap Edit
Scroll to Linked Contacts
Tap Add Contact
Select the duplicate contact to link it
Tap Done to save
Repeat for other duplicate entries if needed