"Sabotage two alarm bells" is an optional mission objective in Sequence 3 / Memory 05: Sugarcane and its Yields
Walkthrough[edit]
To sabotage an Alarm Bell, you need to get close to it and press the action button
Be careful not to be spotted - use Stalking Zones to remain hidden as you approach the alarm bells
Stealthily assassinate any guards or patrols in the area.
Also watch for the gunner in the watchtower. Make your moves only when he turns away