How/ Where do you go to study for the STAMP test?

I’m going to take the STAMP test for japanese later this year in april, i used to go to a private japanese school and id consider myself fluent enough to get by. The problem is that it’s been years since i’ve really used the language and i want to take the test to get highschool credits but im not confident in my ability to pass. Where do i go/ What do I do to study?