Hello gymshoey
Welcome to the SBB Community.
Kindly note, this customer support page is run by volunteer travel experts and passionate SBB clients both sharing their knowledge and experience. We are not the SBB customer service, however.
If you wish official advice, please contact SBB by phone (+41 51 225 78 56) (24/7) or chat (ask the bot to connect you with an employee):
https://www.sbb.ch/en/help-and-contact/chatbot.html#anchor4
That said, here is my reply to your question.
It means that luggage can be sent to Sils/Segl at the “station to station” rate, although it is rather a station to home delivery; thus, the luggage will be delivered directly to the customer’s accommodation at no extra charge.
For transportation, please affix your vacation home (or hotel) address manually to the luggage.
Online pre-order of the return transportation is not permitted for luggage sent to Sils.
You shall purchase the return transportation directly at the Tourist Information in Sils. If you have any questions: +41 81 838 50 50 (Tourist Information Sils).
You might want to double-check with the Tourist Information anyway.
https://www.engadin.ch/en/tourist-information/sils-tourist-information
Kind regards,
Roland