Can I discontinue B.Tech and join in BBA now?

Obviously, you can but the main question is it a right decision or not? Follow some step to analyse. If you want change your course only due to homesickness then I don't think this one as a good decision because up to how much time you will this problem of homesickness after few years you have to g

Yes , you can join BBA after discontinued your b.tech. But before you join think about it . Is is right decision to discontinue b.tech