In order to unlock the tuning and mechanic features, there are some requirements:
1) At least one of your Sports class or above cars needs to be at 8 stars (max blueprints).
2) At least one of your Sports class and above cars needs to have all Black edition parts (it's one step above legendary) all at their maximum ratings.
3) The above two requirements are non optional if you want either one of them to show up and work.
Tuning will only be available for cars that have reached their maximum rating for both stars and parts.
You can level up your legendary parts the same way with any other level through the tuner kits and parts in tuner trials.
Please be aware though, the tuner trials for the legendary part require a Dodge Viper with around 830 PR to complete easily and the Black Edition tuner trials require a Pagani Huayra with about 870 PR to complete relatively easily.
It will take some time to gather the necessary parts and in-game cash, please try not to get too frustrated- too much stress is bad for you.
Hope this helps!
