This article explains how to tag people on your Instagram photos.
Login to Instagram on your mobile device.
Tap on your profile Icon.
Select which photo you would like to Tag someone in.
On the selected photo, Tap the 3 dot icon.
Tap on the Edit button.
Tap on the Tag People area.
Tap on photo to tag people.
Insert name of person you want to tag.
Tap on the name of the person you want to tag.
Your Photo is now tagged.