While it’s not officially supported right now it is possible to arrange pickup and delivery to yourself through your dashboard. If you want to request a delivery from someone else, you simply put their details as the ‘Sender’, and your details as the ‘Receiver’. In this case, you would pay for the order instead of the sender.
Alternatively, it might be easier for the sender to sign up for their own Sendle account.
Note that the sender will still get an email to say that they are sending something to you, so make sure that they know what is going on and are able to print the label and have the package ready for collection.