How do paste to multiple input?

To get the clipboardData text use ev.originalEvent.clipboardData.getData('text'),
than make sure the trimmed length is exactly 6 characters long and all are digits.
Assign to each input it's new value by splitting the string, and focus the last input:

const $inp = $(".passInput");

$inp.on({
  paste(ev) { // Handle Pasting
  
    const clip = ev.originalEvent.clipboardData.getData('text').trim();
    // Allow numbers only
    if (!/\d{6}/.test(clip)) return ev.preventDefault(); // Invalid. Exit here
    // Split string to Array or characters
    const s = [...clip];
    // Populate inputs. Focus last input.
    $inp.val(i => s[i]).eq(5).focus(); 
  },
  input(ev) { // Handle typing
    
    const i = $inp.index(this);
    if (this.value) $inp.eq(i + 1).focus();
  },
  keydown(ev) { // Handle Deleting
    
    const i = $inp.index(this);
    if (!this.value && ev.key === "Backspace" && i) $inp.eq(i - 1).focus();
  }
});
.passInput {
  text-align: center;
  width: 20px;
}
Copy and paste into any field: 456123<br>
Than try with some invalid string: aA123B

<form action="" role="form" method="post" id="passForm">
  <input type="text" class="passInput" name="pass[]" maxlength="1" autocomplete="off" required pattern="\d{1}" autofocus>
  <input type="text" class="passInput" name="pass[]" maxlength="1" autocomplete="off" required pattern="\d{1}">
  <input type="text" class="passInput" name="pass[]" maxlength="1" autocomplete="off" required pattern="\d{1}">
  <input type="text" class="passInput" name="pass[]" maxlength="1" autocomplete="off" required pattern="\d{1}">
  <input type="text" class="passInput" name="pass[]" maxlength="1" autocomplete="off" required pattern="\d{1}">
  <input type="text" class="passInput" name="pass[]" maxlength="1" autocomplete="off" required pattern="\d{1}">
  <button type="submit" class="btn btn-lg btn-primary">SUBMIT</button>
</form>

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