First set the Lifecycle to track: Player Knocks Out. The set trigger to not be visible in game and have it not trigger by collision. Then Wire it to the Trigger: Event Occurs > Trigger.
It should look something like this but you can change the Granted items channels and the numbers. Then put item granters that grant their item after they receive on the channel that you put in the triggers code. (You can use this to remove random items too)
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Great guide!
This has already been made though, you might want to credit this guide by mysz.
You could simplify the code with concatenation to look like this:
set [Variable] to random integer from # to #
Broadcast message on channel | Create text with "RandomItem"
[Variable]
The randomizer will broadcast on “RandomItem” and the number it rolled, then you can make Item Granters that grant when receiving on the channels RandomItem1, 2 etc.