Question

they came to the concert late, so they didn't have good seats
=> If

Answer 1

they came to the concert late, so they didn't have good seats
=> If they had come to the concert soon, they would have had good seats.

Answer 2

If they come to the concert soon, they have good seats.

Answer 3

they came to the concert late, so they didn't have good seats
=> If they hadn't come to the concert late, they would have had good seats.