It depends what you want to do for instance if you want to use it as a career helmet you have to replace the generic helmet file that corresponds to the career helmet you have chosen ingame.
As far as the three files go it would be for example, com_06_helmet_d.tga (this is the career helmet I use).
The video at the following link has a good tutorial on how to do it:
As far as the three files go it would be for example, com_06_helmet_d.tga (this is the career helmet I use).
The video at the following link has a good tutorial on how to do it:
http://www.racedepartment.com/downloads/2017-career-helmet-template.16870/