You cause your code has no checks after the second prompt. In this scenario, You should write your code in a kind of recursion way. When the password check fails, It should begin the same process again and again until it passes.

// fn: verify the password
function verifyPassword(pass) {
  if (pass === "sifra") {
    alert("Correct");
  } else {
    // prompt the password again if it's incorrect
    promptPassword("Incorrect password: ");
  }
}

// fn: promoting the password
function promptPassword(msg = "Enter password:") {
  var pass = window.prompt(`${msg} `);

  // verify the password
  verifyPassword(pass);
}

promptPassword();

This is happening because second time its just taking input but not validating password if you want to validate password untill its correct you can try this just add a loop

var pass = window.prompt("Enter password: ");
while (pass !== sifra) {
  pass = window.prompt("incorrenct password try again: ");
}
// reaches here only when password is corrent