A student obtains a blurred image of a distant object on a screen using a convex lens. To obtain a distinct image on the screen he should move the lens

We must know that – the rays parallel to the principal axis, after refraction by convex lens, will pass through the principal focus. And the incident rays coming from the distant object will be parallel to the principal axis.
Hence, a distinct image will be obtained immediately when distance between screen and lens is equal to focal length.