The LCP element is typically the largest image or text block visible within the viewport of the page. When you run next dev, you'll see a console warning if the LCP element is an <Image> without the priority property.
Once you've identified the LCP image, you can add the property like this:
app/page.js import Image from 'next/image'
import profilePic from '../public/me.png'
 
export default function Page() {
  return <Image src={profilePic} alt="Picture of the author" priority />
}
See more about priority in the next/image component documentation.
Image Sizing