Gear theme – how to add own fields (details listing)

Hello!
I just found this wonderful http://jinsonathemes.com/fabs/?themedemo=Gears theme. I wonder is there a possibility to add own fields?
Car price, model, color, transmission and fuel type is not enough.
I know I can add own fields with basic “add own field” but they are not visible in the theme and I want them permanently there.

I guess it requires some hard coding… but where?
I found something in theme folder/lib files. But will it work if I double the amount of “Car model” text fields and then change name only to mine?

Help 😉
Greetings!