Plugin is already Installed in your both Applications. But You need to Add your GOOGLE_MAPS_ANDROID_API_KEY & GOOGLE_MAPS_IOS_API_KEY in your app-source-code/config.xml
Note: If you donot need the native google maps. Then remove this plugin using the below command.
ionic cordova plugin rm cordova-plugin-googlemaps
Here is the official link with the detailed demonstration of Google Map integration
Link for Google Map Api.