<table>
<tr class="tab">
<td class="one">3</td>
<td class="one">4</td>
<td class="tab1">info</td>
<td class="tab2">9</td>
</tr>
<tr>
<tr class="tab">
<td class="one">3</td>
<td class="one">4</td>
<td class="tab1">info</td>
<td class="tab2">9</td>
</tr>
<tr>
<tr class="tab">
<td class="one">3</td>
<td class="one">4</td>
<td class="tab1">info</td>
<td class="tab2">9</td>
</tr>
</table>
<script>
document.querySelectorAll('td.one').forEach(el => {
el.insertAdjacentHTML('afterend', '<td class="number">' + el.textContent + '</td>');
});
</script>