Remove App from the Apple App Store
To remove your app from the App Store, first go to the URL https://appstoreconnect.apple.com/login and log in with your Apple ID. Then click on My Apps and select your app.
Under the item Pricing and Availability -> Price Schedule -> Availability you will find the command Remove from sale. Confirm this and your app will be removed from the store.
Remove App from the Google Play Store
To delete your app from Google, please follow these steps:
Log in to the Google Play Console using this link here: https://play.google.com/apps/publish. First select the app you wish to remove.
Now go to the Release section, select Setup -> Advanced settings. On the right you will find the App Availability section. Click on Unpublished. This command will delete your app from the Google Play Store.