I went to Japan, changed my store to Japan and added a prepaid credit card to purchase apps. Now I am back in Dubai and I can't change the store to Dubai now. My WhatsApp is about to expire in 1 day.
you probably have money left on your Apple account which you created in Japan. the other possibility is that you may have some subscriptions to which you subscribed in Japan (for example, Apple Music, any news papers and so on).
so you would have to spend all that money or unsubscribe to be able to change the store