Change the date on a scheduled payment

Here's a link in how to do it.

https://www.t-mobile.com/support/account/whats-impacting-your-bill#fourthheading

Yeah, I wanted to make this change online. Didn't need to get hung up going through there phone help. Thanks

You need to call Tmobile to change your billing date and you can only do it once in the lifetime of  the contract.