depends which kind of code you have
if you have a code from purchasing her album off her myplay site and are a part of kellebrities (free to join) you click here and are allowed 2 hours of access before they become available to everyone else. other than that i think it’s just general access to tickets (although i’m not 100%).
kellebrities isn’t the only place to purchase. ticketmaster has some presale codes as well (depends on each date) and you can see which stops have presales here. they might take you to partner sites (livenation and other ones) and will give instructions as to when you can purchase tickets.