Answers can take time to arrive, and many times not at all.
My advice would be to do it in a new blueprint.
As what to do in the blueprint, no-ones really gonna walk you through it (referring to how to make it yourself not the car project demo), at least not in serious detail, so you’ll have to try to break things down further and implement it yourself. (Or follow a tutorial)
So lets talk about the basic stuff you’re looking for.
The vehicles seem to hover, so my first step would be to figure out how to make something hover, then try to add some movement, then make it so that the player causes the movement, then make a track see how it does. Always tweaking and expanding.
Looking deeper at how to make something hover, well all we really need is for the vehicle to roughly stay at a certain height above the ground, so we gotta do some measurements, is it too close to the ground? More force in the +Z direction (Up). Too high? Lets let gravity handle things.
How could we get such measurements, there’s a thing called a raycast, we use that, get the distance to the ground and then apply the previous logic.
I know it’s difficult, heck, I’m not too good myself, but I feel I have a handle on how UE works and how to go about things (game logic and such), sure, they may not be the best, but it works.
I also find it easier, when Googling (I’m assuming you tried) to try and be more specific, like “UE4 how to make object hover”
And to get you started, came across this searching that: https://www.youtube.com/watch?v=5kltaGld6fQ
Hope it at least points you in a better direction.