How can I change the billing date for my apple account

If you're talking about a subscription you would have to cancel the subscription, wait for it to end, then start it again on the desired date.

View, change, or cancel your subscriptions - Click on the link to learn "How to cancel a subscription from Apple." --> https://support.apple.com/HT202039

To solve any immediate need read the links below.

- Create and add money to an iTunes Pass - "At Apple Stores and select retailers, you can add store credit directly to the Apple ID that you use for App Store, iTunes Store, and iBooks Store purchases." - https://support.apple.com/HT203021

- Redeem App Store & iTunes Gift Cards, Apple Music Gift Cards, and content codes - https://support.apple.com/HT201209

You cannot.