If you haven't done so already, create a class MyApplication extends Application for your app, and make sure you add it to your manifest as below (the property that matters here is android:name, I've removed the other xml properties for clarity).
<application
android:name="mypackagename.MyApplication"
... >
Then, in your MyApplication class, create a method getTracker as per Google Analytics v4 documentation https://developers.google.com/analytics/devguides/collection/android/v4/#tracking-methods
Then, use
Tracker t = ((MyApplication) getApplication())
.getTracker(TrackerName.APP_TRACKER);