The currency can be changed via your Google Play/ Apple ID account settings, by changing your country or region. Please see below for instructions.
Play Store
1. Open the Play Store on your device and tap your profile icon (top right corner).
2. Go to settings > general > account and device preferences > country and profiles.
3. Select the country registered to your card.
If you do not, see an option for that country, you will need to add the payment method associated with it. You can only change the country associated with your account once per year.
For more information visit the Google Play help page here.
iOS
1. Go to your device's settings and tap your name.
2. Tap media and purchases > view account > country/ region.
3. Tap change country or region and select the country you wish to use (this must match the billing address registered to your payment method).
4. Review and accept the T&Cs.
5. Select the payment method associated with the selected country.
6. Enter your payment information and tap next.
Before changing the country/region on your account, you will need to spend any remaining store credit. Subscriptions will be canceled upon changing the country/region.
For more information visit the Apple support page here.
Steam
To change the currency in Steam, follow these steps: