JSFiddle - React, Tailwind, and code Playground

HTML

<select>
    <option value="1">1</option>
    <option value="2">2</option>
    <option value="3">3</option>
    <option value="4">4</option>
    <option value="5">5</option>
    <option value="6">6</option>
    <option value="7">7</option>
</select><br />

<table>
    <tbody>
        <tr><td><input type="text" name="teilnehmer1" /></td></tr>
    </tbody>
</table>

JavaScript

$('select').change(function () {
    var count = $(this).val();
    var i = 0;
    $('table').find('tbody tr').each(function (idx) {
        if(idx > count - 1) {
            $(this).remove();
        }
        i = idx;
    });
    for(i; i < count-1; i++) {
        $('table').append('<tr><td><input type="text" /></td></tr>');
    }
    $('table').find('tbody tr td input').each(function (idx) {
        $(this).attr('name',idx + 1);
    });
});