Click on Packages button on the left pane and then click Sent.
Here, you will be able to see the deliveries sent by you. You can also search by the package name or email address in the search bar located at the top right of the page.
Once you have located your delivery, click on More Details button (three dots) on the right which will open a pop-up card.
Here, you will be able to see a lock icon beside each recipient whom you have sent the delivery. Clicking on it will open a password field.
You can either enter a value in the field and hit Set Password, or clear an existing password by clicking Clear Password button. The changes take effect immediately.
You can set different passwords for different recipients. Please note that you will have to supply the new password via your preferred means of communication.