Hi @elainesb1, welcome to TPG Community!
Check out this article on how to top up your mobile prepaid balance. This will show you the screenshots that you should be seeing after you login to your account. https://community.tpg.com.au/t5/Accounts-and-Billing/How-To-Top-Up-TPG-Mobile-Prepaid-Balance/m-p/10...
If you need further help, you can send us a private message with your details.