#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 5;
char a[65];
void pre() {
  int j = 1;
  for (j = 1; j <= 10; j++) a[j - 1] = (char)(j - 1 + 48);
  for (int i = 0; i < 26; i++) a[j++] = (char)(i + 97);
  for (int i = 0; i < 26; i++) a[j++] = (char)(i + 65);
  a[10] = 'Z';
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  pre();
  int T;
  cin >> T;
  while (T--) {
    vector<int> val(65, 0);
    int r, c, k;
    cin >> r >> c >> k;
    string s[r], ans[r];
    int R = 0;
    for (int i = 0; i < r; i++) {
      cin >> s[i];
      for (int j = 0; j < s[i].size(); j++) {
        if (s[i][j] == 'R') R++;
        ans[i] += '.';
      }
    }
    int x = R / k;
    R = R % k;
    for (int i = 0; i < k; i++) {
      val[i] = x;
      if (R) {
        R--;
        val[i]++;
      }
    }
    int gg = 0;
    for (int i = 0; i < r; i++) {
      if (i % 2 == 0) {
        for (int j = 0; j < c; j++) {
          ans[i][j] = a[gg];
          if (s[i][j] == 'R') {
            val[gg]--;
            if (!val[gg]) {
              gg++;
            }
          }
          if (gg >= k - 1) gg = k - 1;
        }
      } else {
        for (int j = c - 1; j >= 0; j--) {
          ans[i][j] = a[gg];
          if (s[i][j] == 'R') {
            val[gg]--;
            if (!val[gg]) {
              gg++;
            }
          }
          if (gg >= k - 1) gg = k - 1;
        }
      }
    }
    for (int i = 0; i < r; i++) cout << ans[i] << "\n";
  }
  return 0;
}
