There are two ways really. The first way would be to go through the long process of going through all your sale confirmation emails from us and then filtering out all the buyers who bought that specific digital product in the past. Indeed this would be very time consuming.
However, if like us, you like more efficient ways to do thing, then the simplest way would be to just update the product in your plug&paid inventory page.
1. Go to your inventory page and Edit the digital product.
2. Once the product editor is open, hit the 'Upload' icon and select the file you wish to update the product with. Do not forget to hit 'Save' to apply your changes!
3. When saving your file, you will be prompted as to whether you wish to send the updated file to your existing buyers. Choose between YES or NO.
The new file will be sent to the buyer's email address which was used to purchase the product.
In three simple steps you are done!