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You will need to wait for the new garage update to be released to you before you can park your car in rally. Once you have the new garage you can choose what car you would like to use.
The concept car is a vehicle that you can customize to look like a tank, a pirate ship, a mecha head, etc etc by using special skins you can find in the marketplace. Most of these are a bit pricey, though.
As a side note, you don't need to make a new thread for every rally-related question you have. Most of your questions are the same and have the same solution. You can add questions to existing threads by using the edit feature. This will make finding answers easier for you and will prevent forum clutter.
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