Unfortunately in PowerApps you cannot assign values by simply using the = operator. So saying Label.Text = "John" will do nothing etc.
Here is a test I did to explain how this can work:
Dropdown 1 items set to: ["Choice 1","Choice 2","Choice 3","Choice 4","Choice 5"]
Dropdown 2 items set to: ["one","two","three","four","five"]
Dropdown 2 default set to: Switch(Dropdown2.Selected.Value, "Choice 1", "one", "Choice 2", "two", "Choice 3", "three", "Choice 4", "four", "Choice 5", "five")
When I select "Chocie 3", the second dropdown changes to "three", when I change it to "Choice 1" it changes dropdown 2 to "one".
