Ah, this problem occurs because the lining of the collar has shrunk at a more advanced rate to the outer side - causing the ripples.

There really is no way to repair the damage, but you can definitely minimise how noticeable it is by the way you iron your shirt. You should lay the collar flat on the ironing board, then iron from the outside inwards, pushing the ripples towards the centre. This way when you flex the collar some of the ripples should disappear into the bend.

Hope that helps!