use proconio::{input, marker::Bytes};

fn main() {
    input! {t:usize}
    for _ in 0..t {
        input! {n:usize, mut s:Bytes}
        let mut l = false;
        for i in 0..n {
            let flip = if i == 0 {
                s[i] != b'A'
            } else if i == 1 {
                s[i] != b'B'
            } else {
                s[i] != b'A'
            };
            if flip {
                l = true;
                s[i] = if s[i] == b'A' { b'B' } else { b'A' };
            } else if l {
                break;
            }
        }
        s[0] = b'B';
        println!("{}", String::from_utf8(s).unwrap());
    }
}