#include <bits/stdc++.h>
using namespace std;
template <typename T>
void maxtt(T &t1, T t2) {
  t1 = max(t1, t2);
}
template <typename T>
void mintt(T &t1, T t2) {
  t1 = min(t1, t2);
}
bool debug = 0;
int n, m, k;
int dx[4] = {0, 1, 0, -1}, dy[4] = {1, 0, -1, 0};
string direc = "RDLU";
long long ln, lk, lm;
void etp(bool f = 0) {
  puts(f ? "YES" : "NO");
  exit(0);
}
void addmod(int &x, int y, int mod = 998244353) {
  assert(y >= 0);
  x += y;
  if (x >= mod) x -= mod;
  assert(x >= 0 && x < mod);
}
void et(int x = -1) {
  printf("%d\n", x);
  exit(0);
}
long long fastPow(long long x, long long y, int mod = 998244353) {
  long long ans = 1;
  while (y > 0) {
    if (y & 1) ans = (x * ans) % mod;
    x = x * x % mod;
    y >>= 1;
  }
  return ans;
}
long long gcd1(long long x, long long y) { return y ? gcd1(y, x % y) : x; }
bitset<2135> bs[2135];
char ins[2135];
int f[2135], cc[2135];
vector<pair<int, int>> es;
int ff(int x) { return x == f[x] ? x : f[x] = ff(f[x]); }
void clr() {
  es.clear();
  for (int(i) = 1; (i) <= (int)(n); (i)++) bs[i].reset();
}
void fmain(int tid) {
  scanf("%d%d", &n, &m);
  for (int(j) = 1; (j) <= (int)(m); (j)++) {
    scanf("%s", ins + 1);
    cc[j] = 0;
    for (int(i) = 1; (i) <= (int)(n); (i)++) {
      if (ins[i] == '1') {
        bs[i][j] = 1;
        cc[j]++;
      }
    }
  }
  vector<pair<int, pair<int, int>>> vp;
  for (int(i) = 1; (i) <= (int)(n); (i)++)
    for (int(j) = 1; (j) <= (int)(n); (j)++) {
      int z = (bs[i] & bs[j]).count();
      vp.push_back({-z, {i, j}});
    }
  for (int(i) = 1; (i) <= (int)(n); (i)++) f[i] = i;
  sort(vp.begin(), vp.end());
  for (auto &p : vp) {
    int x = p.second.first, y = p.second.second;
    int fx = ff(x), fy = ff(y);
    if (fx == fy) continue;
    f[fx] = fy;
    es.push_back({x, y});
  }
  bool ok = 1;
  for (int(j) = 1; (j) <= (int)(m); (j)++) {
    int z = 0;
    for (auto &p : es)
      if (bs[p.first][j] && bs[p.second][j]) {
        z++;
      }
    if (z != cc[j] - 1) {
      ok = 0;
      break;
    }
  }
  if (!ok)
    puts("NO");
  else {
    puts("YES");
    for (auto &p : es) printf("%d %d\n", p.first, p.second);
  }
  clr();
}
int main() {
  int t = 1;
  scanf("%d", &t);
  for (int(i) = 1; (i) <= (int)(t); (i)++) {
    fmain(i);
  }
  return 0;
}
