Players who purchased Rocket League before the Free to Play update get Chopper Wheels as a veteran perk! Follow these steps to claim your wheels:

Register for an Epic Games account

Link your original platform account to your Epic Games account

Download the Epic Games Store Launcher

Launch the Epic Games Store

Select Store from the side menu

Search for Rocket League.

Click Get to add Rocket League to your account

Launch Rocket League from Epic Games Store

The Chopper Wheels will be added to your account once Rocket League has been launched from your Epic Games Store account.