Firstly would want to reset my Apple wallet balance to zero and

Re: "Firstly would want to reset my Apple wallet balance to zero"

Seems it would be your Apple Account that needs the zero balance. (Apple Wallet has cards for Apple Pay)

Here are a couple of ways to choose from:

(1) You can purchase an item that costs more than your balance and use a payment method for the rest.

or

(2)" If your balance is less than the cost of a single item, contact Apple Support."

(The link above connects you to where you can Sign in and zero your account) losing any money left.

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Re: "Secondly I can’t see my region nigeria on apple so how do i subscribe for Apple Music"

See how to: Subscribe to Apple Music - Apple Support

and

Apple Support's online article: Availability of Apple Media Services - Apple Support

Eg: says items listed below are available::

Nigeria

• App Store
  • Apple Arcade
• Apple Music
  • Apple Music Classical
• iTunes Store Music purchases
• Shazam
• Apple TV app
  • Synced videos only
• Apple Books
  • Public domain books only
• Apple Podcasts
• Ringtone & Tone purchases