#include <bits/stdc++.h>
using namespace std;
long long n, k, m, s, t;
char a[1010];
signed main() {
  cin >> t;
  while (t--) {
    memset(a, 0, sizeof(a));
    cin >> n;
    for (long long i = 1; i <= n; i++) {
      cin >> a[i];
    }
    char c = 'B';
    for (long long i = 1; i <= n; i++) {
      if (a[i] != '?') {
        if (a[i] == 'B' && i % 2 == 0) c = 'R';
        if (a[i] == 'R' && i % 2 == 1) c = 'R';
        break;
      }
    }
    for (long long i = 1; i <= n; i++) {
      if (a[i] != '?') {
        if (a[i] == 'B')
          c = 'R';
        else
          c = 'B';
      } else
        a[i] = c;
      if (a[i] == 'B')
        c = 'R';
      else
        c = 'B';
    }
    for (long long i = 1; i <= n; i++) cout << a[i];
    cout << endl;
  }
}
