How do I accomplish this in Construct 3 with the new functions?
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You can refer to the manual article for functions : https://www.construct.net/en/make-games/manuals/construct-3/project-primitives/events/functions
Make sure to add a parameter of the name you feel appropriate to represent the value you are passing to your function.
In your "Pick with UID" condition, go and select the parameter from the global/local variable spot in the System object.