In the Return Summary on the last page of the return, click your cursor in the 'Under Threshold Amount' box, you will be able to input data in this field.
If you have '0' showing in the 'Amount' box, then you can simply enter your Total Receipts figure in the 'Under Threshold Amount' box.
If you a have a figure showing in the 'Amount' box - this figure represents the total of all the amounts you have disclosed using the 'Receipts' button on the first page of the return. To enter your Total Receipts, deduct the 'Amounts' figure from your Total Receipts figure. The difference between these figures should be entered in the 'Under Threshold Amount' box. The 'Total Amount' box should now show your Total Receipts figure.