Open the Photos app
Select the photo
Tap Edit
Use the Depth Control slider if available to blur the background
Use Portrait mode photos for stronger background blur
Tap the aperture icon to adjust blur level
Save the edited photo
If you need manual blur, open the photo in a third-party app like Snapseed, Canva, or Photoshop Express
Use the blur tool in the app
Apply the blur to the area you want
Save or export the edited photo