How can you set up and install tracking for mobile apps?

1-Enable app install tracking in your account.
2-Update your Analytics SDK.
3-Set up Custom Campaigns.

It seems a bit complicated, but each one takes a short time.

Navigate to the property you want to edit in the Admin panel of Google Analytics.
Then click "Property Settings"
In the "iOS Campaign Tracking" section, click the toggle to turn it "ON"
Click Save
Then you need to update your Analytics SDK.
To do this, you should add the Firebase SDK to your new or existing iOS app. You can see how to add this in a detailed way from here.