How on earth can I use the junkman parts on the carreer mode?

When you get the junkman parts go to a proformance shop then when your in there you will have an option that says backroom press circle and there you have it you'll be able to use your junkman parts. Hope i've helped ya

When you defeat a blacklist rival, and you get to pick two markers, the three on the right are for special mods, and one of them says perf. Mod, one says visual mod, and one says something else

In the customise cars option (not in career mode) every part is available for use. Though, in career mode, you must earn your junkman parts by getting them from the bonus markers from rivals on the blacklist. Once you have one, press o (circle) to go the backroom where you can use them.

You earn the markers from the blacklist members.

I made my junkman cheat at the start..But when I go to my cars "not my carear" thay aren't there..
What going on?

When you put the burgerking code in the start........you have to go to challenge series and beat the last challenge called burgerking(unlocked because of the cheat code) after beating it the parts become available.