According to the response from the senior consultant of Budweiser International Education, you don't need to reply anything. You have been accepted, so you don't need to reply to the email like a conditional admission.
Unless you want to change your major again, you need to contact the school in advance and apply for changing your major.
There is also a notice from the school in the form of mail. When the visa is approved, your mail will be approved.
Budweiser International Education recommends that you get in touch with the school after receiving the email, and ask and confirm your admission and accommodation first.
Make full preparations for studying abroad.
On the visa issue, that university doesn't know when your visa will expire or whether you are at home or abroad, so communicate with the school in advance about the visa and other matters.
Congratulations!