#include <bits/stdc++.h>

using i64 = long long;

void solve() {
    int n;
    i64 k;
    std::cin >> n >> k;

    std::string s;
    std::cin >> s;

    if (n == 1) {
        s[0] ^= k % 2;
    } else {
        i64 c = 0;
        for (int l = 0, r; c < k && l < n; l = r) {
            for (; l < n && s[l] == '1'; ++l);
            for (r = l; r < n && s[r] == '0'; ++r);
            std::fill(s.begin() + l, s.begin() + r, '1');
            c += l < r;
        }
        if (k == 1 && c == 0) {
            s.back() = '0';
        }
    }

    std::cout << s << '\n';
}

int main() {
    std::cin.tie(nullptr)->sync_with_stdio(false);

    int t;
    std::cin >> t;

    while (t--) {
        solve();
    }

    return 0;
}