I usually spray on aone of the fragrances that my cousin gave it to me years ago, t. They are good scents, but I don’t know their names. I usually spray on one of the fragrances that my cousin gave me years ago. They are good scents, but I don’t know their names.

The first part of your sentence is talking about one fragrance, but the ending mentions plural fragrances. I edited the first part to agree with the end part. We are still talking about "fragrance," so you don't need the word "it" in the same sentence.

I usually spray on a fragrance that my cousin gave it to me years ago, t. They are goodexcellent scents, but I don’t know their names (unfortunately). I usually spray on a fragrance that my cousin gave it to me years ago. They are excellent scents, but I don’t know their names (unfortunately).

I think there are a lot of people who add scents to themselves with body soap instead of a fragrances in Japan. I think there are a lot of people who add scents to themselves with body soap instead of fragrances in Japan.

Speaking about many different people, I would put scents and fragrances as plural, not to mean that individuals are using multiple of either, but because we are referencing multiple of both as a whole / speaking in general

I think there are a lot of people who adduse scent themselves withed body soap instead of a fragrance in Japan. I think there are a lot of people who use scented body soap instead of a fragrance in Japan.