Welcome to the Community @olfil
In setting up the TPG email, here are the articles that we've created that customers may use as a guide.
Customers may also check our online guide : https://www.tpg.com.au/support/emailsetting.php
If you are going to setup your main TPG email account, then you need to use your TPG username. If you want to change the name on it, then you might need to create an Alias. You may check this previous post on how to create an Alias.