In Elixir, to perform a join on tuples, you can use the Tuple.join/2 function. This function takes two tuples as arguments and joins them together into a single tuple. For example, if you have two tuples tuple1 = {:a, :b} and tuple2 = {:c, :d}, you can join them like this: Tuple.join(tuple1, tuple2), which would result in {:a, :b, :c, :d}.