The procedure for updating Home Assistant on Synology Docker has changed. Synology Docker 20.10.3-0554 (June 2021 update) changed the relevant Action menu item from "Clear" to "Reset".
Old Documentation:
Right-click on it and select “Action”->“Clear”
Proposed New Documentation:
Right-click on it and select “Action”->“Reset”
Found solution here:
https://www.reddit.com/r/synology/comments/ocwj2e/docker_action_clear_now_action_reset/