App store credits

—First—

Make a request to zero out any remaining balance on your account by contacting Customer Support by phone or chat:

• Call 1-800-APLCARE. 📞
• International Support. 🌐
• Contact Apple Support. 📝
• Live chat using Messages. 💬

—Next—

Cancel your subscriptions and wait until the end of the subscription period. 

—Then—

Click ▶︎ Change Region. 🌐

Either spend it, or if your credit is less then the cost of a single item, ask iTunes Store support staff to zero out your balance for you

iTunes - Official Apple Support