how do you set a specific collision box to be interacted?

I think @Ligazetom is just saying you’ve got the thing back to front.

You’re doing it so the player presses ‘use car’ and then your system looks for overlaps etc.

But maybe you need to drive ( pun intended ) the whole thing from the other end. When something overlaps with the car door, you check if it’s the player, if it is, you ask them if they want to get in.