For dataflow programming, you introduce structures. For example, in LabVIEW, one has many types of structures such as for loops, while loops, case structures (for making decisions), event structures (for listening to and responding to user events), type specialization structures (for reacting, at development/compile time, to types in a dynamic way as a type of development/compile time polymorphism), conditional compile structures (for conditionally compiling different parts of code), and disable structures (for disabling certain parts of code).

Here's a simple case structure for a decision based upon a boolean value: https://imgur.com/a/YyzXVhU

This is really no different than the type of dataflow you have in other functional languages like F# or Racket. Values flow into special syntax forms such as if or match that allow branching.