Resilio Connect is not published in Synology's Package Center, so it needs to be installed manually.
To do that follow the steps:
1. Download the agent config from Management Console. Refer to this article for more information.
2. Login to Synology Web UI and open File Station. Click Create > Create New Shared Folder:
3. Set new name for the folder to be "Resilio Agent" (mind the case and space, watch out for trailing spaces):
4. On the next step enable Read/Write permissions for "admin" user:
5. Name the downloaded config file as "sync.conf" and put into this directory:
6. Download the appropriate package for your Synology architecture. List of all architectures to verify can be found here: https://www.synology.com/en-global/knowledgebase/DSM/tutorial/General/What_kind_of_CPU_does_my_NAS_have
7. On NAS go to Package Center -> Manual Install:
8. Pick the downloaded spk, agree to possible "Digital signature" exception and proceed:
9. Check "Run after installation" checkbox and click Apply button:
10. If everything set up correctly then Resilio Agent status will be running:
The agent will pickup the config and automatically connect to the Console. Config file will be moved to the Agent's storage. Thus "sync.conf" will disappear from Resilio Agent folder and Downloads folder will appear there: