The Invisibility spell ends when the target attacks or casts a spell:
The spell ends for a target that attacks or casts a spell.
The "Tentacle Rod" magical items lets the user direct three tentacles to attack target(s):
While holding the rod, you can use an action to direct each tentacle to attack a creature you can see within 15 feet of you. Each tentacle makes a melee attack roll with a +9 bonus. On a hit, the tentacle deals 1d6 bludgeoning damage. If you hit a target with all three tentacles, it must make a DC 15 Constitution saving throw. On a failure, the creature's speed is halved, it has disadvantage on Dexterity saving throws, and it can't use reactions for 1 minute.
Does activating the Tentacle Rod break the invisibility spell? I'm not sure if "directing each tentacle to attack" counts as attacking yourself.