To set up a forwarding order with an alternative postal carrier, follow the instructions on your carrier's website. When entering the address for the new receiving address, enter your CAYA mailbox address, which can be found in your account settings.
For more information, see this article: What is my postbox address?
(For more on this, see the article: My mailbox address was at Glogauer Str., now the address has changed. Does my mail still arrive, what can I do?)