#include <bits/stdc++.h>
const long long int mod = 1e9 + 7;
const long long int inf = 1e17;
const double pi = 3.1415926536;
using namespace std;
using namespace std::chrono;
long long int biExp(long long int a, long long int b) {
  if (b == 0) return 1;
  if (b % 2 == 1)
    return (a * biExp(a, b - 1)) % mod;
  else {
    long long int temp = biExp(a, b / 2);
    return (temp * temp) % mod;
  }
}
long long int ModularInverse(long long a) { return biExp(a, mod - 2); }
long long int power(long long int a, long long int b) {
  if (b == 0) return 1;
  if (b % 2 == 1)
    return (a * pow(a, b - 1));
  else {
    long long int temp = pow(a, b / 2);
    return (temp * temp);
  }
}
string a, b;
long long int get_ans(string str, char st) {
  char ch = st;
  for (int i = 0; i < str.size(); i++) {
    if (str[i] == '?' and i == 0) {
      str[i] = st;
    } else if (i != 0 and str[i] == '?') {
      if (str[i - 1] == 'R')
        str[i] = 'B';
      else {
        str[i] = 'R';
      }
    }
  }
  long long int cnt = 0;
  for (int i = 0; i + 1 < str.size(); i++) {
    if (str[i] == str[i + 1]) cnt++;
  }
  if (ch == 'R')
    a = str;
  else
    b = str;
  return cnt;
}
void tc() {
  long long int n;
  cin >> n;
  string str;
  cin >> str;
  long long int aa = get_ans(str, 'R');
  long long int bb = get_ans(str, 'B');
  if (aa < bb) {
    cout << a << endl;
    return;
  } else {
    cout << b << endl;
    return;
  }
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  ;
  auto start = high_resolution_clock::now();
  long long int t = 1;
  cin >> t;
  while (t--) {
    tc();
  }
  auto stop = high_resolution_clock::now();
  auto duration = duration_cast<microseconds>(stop - start);
  return 0;
}
