You can find the instructions on the page:
https://firebase.google.com/support/guides/disable-analytics
Disable Analytics collection on Android
Temporarily disable collection
If you wish to temporarily disable Analytics collection, such as to get end-user consent before collecting data, you can set the value of firebase_analytics_collection_enabled to false in your app's AndroidManifest.xml in the application tag. For example:
<meta-data android:name="firebase_analytics_collection_enabled" android:value="false" />
To re-enable collection, such as after an end-user provides consent, call the setAnalyticsCollectionEnabled() method of the FirebaseAnalytics class. For example:
setAnalyticsCollectionEnabled(true);
If you need to suspend collection again for any reason, you can call
setAnalyticsCollectionEnabled(false);
and collection is suspended until you re-enable it.
Permanently deactivate collection
If you need to deactivate Analytics collection permanently in a version of your app, set firebase_analytics_collection_deactivated to true in your app's AndroidManifest.xml in the application tag. For example:
<meta-data android:name="firebase_analytics_collection_deactivated" android:value="true" />