<table>
  <thead>
    <tr>
      <th scope="col">Dates and amounts</th>
      <th></th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>First 6 weeks</td>
      <td>£109.80 per week</td>
    </tr>
    <tr>
      <td>Next 33 weeks</td>
      <td>£109.80 per week</td>
    </tr>
    <tr>
     <td>Total estimated pay</td>
      <td>£4,282.20</td>
    </tr>
    <tr>
      <td>Tell the mother’s employer</td>
      <td>28 days before they want to start maternity pay</td>
    </tr>
  </tbody>
</table>

<table>
  <thead>
    <tr>
      <th colspan="2">Dates and amounts</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>First 6 weeks</td>
      <td>£109.80 per week</td>
    </tr>
    <tr>
      <td>Next 33 weeks</td>
      <td>£109.80 per week</td>
    </tr>
    <tr>
     <td>Total estimated pay</td>
      <td>£4,282.20</td>
    </tr>
    <tr>
      <td>Tell the mother’s employer</td>
      <td>28 days before they want to start maternity pay</td>
    </tr>
  </tbody>
</table>

Remove scope="col" and add colspan="2"
Remove scope="col" and add colspan="2"

Add colspan=“2”, as the heading is for both the dates and amounts table
cells underneath
