stolen phone; find my authorization code

so in short someone I know got their phone stolen along with an entire car and I’ve been asked to track an airtag along with a phone that was in the car when it was stolen. Using find my i used their icloud account to sign in but since they don’t have any other devices with their icloud i can’t get past the two factor authentication. We plan to take legal action to get everything back but it would help to still track the phone and airtag.