Synology DS3617xsII Hardware Installation Manual page 13

3 Remove the expansion slot shield:
a Reposition your Synology NAS so that the top will be facing your body, with drive trays on the right side.
b Pull the clip above the expansion slot shield in the direction as illustrated below.
c Remove the shield.
4 Install the network interface card:
a Align the card's connectors with the expansion slot.
13 Chapter 2: Hardware Setup
b
c