Tagging people before sharing a photo or video
To tag someone before sharing a photo or video:
Tagging people after sharing a photo or video
To tag someone in a photo or video you've already shared:

Instagram app for Android and iPhone
Note that if you're tagging someone that is set up as a
creator or
business account, you can also include their profile category by tapping
Tag Category below their name.
If you're not able to tag someone, they may have changed
who can tag them in their privacy settings.