Using a computer, *not cell phone!*, select My account and login. On the left hand side select My Profile. On the right hand side scroll down until you see Transfer My Number. Click that and beging the process. Make sure you are still using your old sim card/network when you respond to the old network by text about transfering. I figured this out with zero help from public mobile as there is no human to speak with and the chat bot/creating a ticket was unfruitful.
