I am a Japanese major. Although I am not a school, I hope it will be useful to you. Now that you have been accepted, it means that they don't need basic knowledge of Japanese, so start from scratch. I didn't learn Japanese when I chose my major. I study English in high school. After I went to college, my classmates also had a foundation in Japanese, but the content of college was not quite the same as that of their high school. Even if there is no foundation, I don't have to worry.