You can find the option that allows you to resend receipts under 'Customer transactions' but also in the 'Support' section.
1. 'Customer transactions' section:
Find the customer for the particular purchase and click on the envelope icon:
Then resend the receipt.
Since the email field is editable you can also resend the receipt to another email address (sometimes it happens that someone had signed up but made a typo in their email address. In that case you are able to resent it to an alternative email address).
2. 'Support' section: Find the customer by their email and click on it.
You'll see their profile with the extension option in it:
Simply click on it to resend the receipt:
*Please note that there is no resend receipt button when customer purchased with e-wallet /credits.