#include <bits/stdc++.h>
using namespace std;
const int N = 105;
int t, n, cnt;
char s[N];
int main() {
  scanf("%d", &t);
  while (t--) {
    cnt = 0;
    scanf("%d", &n);
    scanf("%s", s + 1);
    for (int i = 1; i <= n; i++) cnt += (s[i] != '?');
    if (!cnt) s[1] = 'R';
    for (int i = 2; i <= n; i++)
      if (s[i] == '?' && s[i - 1] != '?') s[i] = s[i - 1] ^ ('B' ^ 'R');
    for (int i = n - 1; i; i--)
      if (s[i] == '?' && s[i + 1] != '?') s[i] = s[i + 1] ^ ('B' ^ 'R');
    printf("%s\n", s + 1);
  }
  return 0;
}
