I attempted to use the disabled attribute on p-tableheadercheckbox in order to activate the checkbox.
<p-tableHeaderCheckbox [disabled]="false"></p-tableHeaderCheckbox>
<ng-template pTemplate="header">
<tr>
<th style="width: 3rem">
<p-tableHeaderCheckbox [disabled]="false"></p-tableHeaderCheckbox>
</th>
<th>Recharge Amount ({{ rupeeSymbol }})</th>
<th>Tag Account</th>
<th>Plate No.</th>
<th>Tag Serial No.</th>
<th>Vehicle Class</th>
<th>Minimum Threshold ({{ rupeeSymbol }})</th>
<th>Current Balance ({{ rupeeSymbol }})</th>
</tr>
</ng-template>