#include <bits/stdc++.h>
using namespace std;
int main() {
  char alfabetGainuse[] =
      "-abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPRQSTUVWXYZ0123456789";
  int T;
  cin >> T;
  for (int t = 1; t <= T; t++) {
    int r, c, k;
    cin >> r >> c >> k;
    char harta[r + 1][c + 1];
    cin.get();
    for (int i = 1; i <= r; i++) {
      cin.get(harta[i], c + 1);
      cin.get();
    }
    int mancare = 0;
    for (int i = 1; i <= r; i++) {
      for (int j = 0; j < c; j++) {
        if (harta[i][j] == 'R') mancare++;
      }
    }
    int mancareGainuse[k + 1];
    for (int i = 1; i <= k; i++) {
      mancareGainuse[i] = mancare / k;
    }
    for (int i = 1; i <= mancare % k; i++) {
      mancareGainuse[i]++;
    }
    char hartaNoua[r + 1][c + 2];
    int indexGaina = 1;
    int mancareGasita = 0;
    for (int i = 1; i <= r; i++) {
      hartaNoua[i][c] = '\0';
      if (i % 2 == 1) {
        for (int j = 0; j < c; j++) {
          if (indexGaina == k + 1) {
            hartaNoua[i][j] = alfabetGainuse[indexGaina - 1];
          } else {
            hartaNoua[i][j] = alfabetGainuse[indexGaina];
            if (harta[i][j] == 'R') {
              mancareGasita++;
              if (mancareGasita == mancareGainuse[indexGaina]) {
                indexGaina++;
                mancareGasita = 0;
              }
            }
          }
        }
      } else {
        for (int j = c - 1; j >= 0; j--) {
          if (indexGaina == k + 1) {
            hartaNoua[i][j] = alfabetGainuse[indexGaina - 1];
          } else {
            hartaNoua[i][j] = alfabetGainuse[indexGaina];
            if (harta[i][j] == 'R') {
              mancareGasita++;
              if (mancareGasita == mancareGainuse[indexGaina]) {
                indexGaina++;
                mancareGasita = 0;
              }
            }
          }
        }
      }
    }
    for (int i = 1; i <= r; i++) {
      cout << hartaNoua[i] << "\n";
    }
  }
  return 0;
}
