To apply the zoom effect on your profile picture, tap and hold the picture on your profile. After a moment, the zoom will activate and you can zoom in on the image to emphasize specific details. While zooming, you can highlight important elements in your profile picture. For example, you could zoom in on your face if you're using a selfie, or on the logo if you're representing a company. When you are satisfied with the zoom effect and positioning, tap "Save" or "Done" to apply the changes. Your profile picture with the zoom effect will now appear on your Instagram profile.