Has your client lost access to their purchase? They should be able to get back in on the same computer they purchased on, but if not, restore purchase allows them to set up a password and get access simply.
How To Allow Restore Purchase
Go to the bot you wish to allow restore purchase on and select the Publishing tab
Make sure your bot is published
Scroll down the bottom of publishing settings where you will see "Allow Restore Purchase"
Check this box
How Your Customer Can Use Restore Purchase
Your customers will see the Restore Purchase button on the details page.
2. Once they select the Restore Purchase button they will be able to enter their email address and create a password.
3. Note, this must be the email address they used to purchase the document.
4. They will now be able to see their previously purchased interviews.