To set up the Tile Mate with an iPhone like the iPhone 6 Plus, you just need to simply download and open the Tile App from the Apple App Store. You'll need to log in with or create a new Tile account.
On the iPhone, you'll need to turn on Bluetooth to communicate with the Tile Mate (see this review to see more on how Tile uses Bluetooth Low Energy). You'll also need to enable location tracking on your phone since the Tile doesn't actually have any location tracking itself. The Tile App uses your phone's GPS location as the location for your Tile assuming both are connected over Bluetooth.
For some reason the Tile App also wants to access the iPhone's Motion and Fitness Activity to help conserve the phone's battery.
The Tile App also tracks all the phones which has the Tile App set up with your Tile account.
You can then select 'Add a Tile' and choose the 'Mate'. To finish the setup, you simply need to click the Tile logo on the Tile Mate.
The iPhone 6 Plus was able to easily connect to the Tile Mate over Bluetooth. You can use the phone to find the Tile by seeing its location on a map or playing a ringtone on the Tile. You can also find your phone by pressing the logo on the Tile Mate a couple of times.