Colour grading advice
First off, I recommend you use davinci resolve for grading (it's also free).
There are two options that you have, you could either draw a mask on the part you want to affect, track that mask to follow the motion and apply the grade only inside of that mask.
Second would be to pick the colour of the area you want to change and only alter this spectrum, which can lead to artifacts, especially when not working with original files tho.