#include <bits/stdc++.h>

using namespace std;

int32_t main() {
  cin.tie(0) -> sync_with_stdio(0);
  int t;
  cin >> t;
  while (t--) {
    int n, k;
    cin >> n >> k;
    string s;
    cin >> s;
    if (n == k) {
      cout << "0\n";
      continue;
    }
    while (k-- > 0) {
      bool done = false;
      for (int i = 1; i < s.size(); i++) {
        if (s[i] > s[i - 1]) {
          s.erase(s.begin() + i - 1);
          done = true;
          break;
        }
      }
      if (!done) {
        s.pop_back();
      }
    }
    cout << s << "\n";
  }

  return 0;
}