How to change the api key preset in app/gradle?

Question

 test {
        versionCode 1
        versionName "0.1"
        applicationId 'com.test.user'
        manifestPlaceholders = [
                onesignal_app_id               : 'one_signal_key',
                onesignal_google_project_number: 'REMOTE'
        ]
        vectorDrawables.useSupportLibrary = true
        resValue "string", "app_name" +
                "", "Test Store"
        buildConfigField("String", "BASE_URL", "base_url")
        buildConfigField("String", "PUBLIC_KEY", "public_key")
        buildConfigField("String", "SECRET_KEY", "secret_key")
        resValue "string", "google_map_key", "api_key"
        buildConfigField("String", "MAP_KEY", "map_key")
        buildConfigField("String", "BUILD_VARIANT", "test")
    }

this is my app/gradle and have created a test flavor.

I will receive the google_map_key from backend and update that key in my app/gradle. How can i achieve this?