If you have added a receipt, but it was not added to the correct report, you may want to move them to the correct report.
First, go to the Receipts tab (bottom left):
Next, tap the report selector:
There are two possibilities here:
If the receipt was added to a different report (e.g. by mistake), select the report to which the receipt is currently assigned.
If the receipt was not added to any report, uncheck the selected report. This will take you to the list of all available receipts.
Swipe left on any receipt you want to move and tap the move button (orange):
Select the report you want the receipt to be added to.