How to Transfer from CA1312 from Guilin to CA421 to Tokyo at Beijing airport?

My son will arive from Guilin with CA1312 which is late. He will have to take the CA421 to Tokyo.
Can you explain the detailed path he will have to take when he leaves the CA1312 plane to reach the correct Gate for CA421 within the time limit ?
Does he have to collect his luggage and get out, then check-in to CA421 ?

Thank you !