IOS IDFA: Firebase and Google Adwords.

Question

I am doing UAC to promote my iOS app. Read the Google documentation and still cannot figure out how and when to use IDFA.

What I've done:
- Added Firebase for my module and done basic configuration, so the first_open events first_open tracked
- Associated Firebase with Adwords
- Setting UAC to convert first_open as conversion

And my question is: what additional configuration is required?
- Do I need IDFA to allow Adwords to recognize first_open events correctly?

- So, should I install the GoogleIDFASupport module?
- Then I use the advertisingIdentifier of the ASIdentifierManager class to get the IDFA string? So what? How to get Adwords and Firebase to find out that first_open is associated with a specific IDFA?

If the IDFA is not required, how does Google know if the first_open event first_open new installation received in UAC instead of an existing update or reinstallation of the application directly from the App Store?

Thanks for all the help, the first day in this, and all this is very confusing.