How do you access your vehicle inventory in Speedway?

I can't figure out how to change my vehicle in Toybox Speedway? Is there a certain feat I have to complete to do this or is there a combination of buttons on the controller? I can't seem to find an answer anywhere on the internet and I'm certain I'm going to feel like an idiot when I see the answer but please help!!

When going towards the race there is a red thing beside the yellow car to summon any vehicle you have


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Also here is a cool trick most people don't know. You can use power disk vehicles too! place a ground based vehicle power disk under the speed play piece and it will summon in.

If you get gold in everything you can use the weapons and boosts in a free play mode. That is something most people don't know

My son loves racing with General Grievous' Wheel Bike.