Look at the name of this block - Modify Variables. Modify... Variables. Variables, not Constants. Even it's color is blue-ish, like the color of Variables. Use Variables in it, not Constants.
Variables are global variables. Constants are the same, but they are those "input" global variables... but not exactly variables, because MQL5 is giving error messages when you try to modify them.
Again, Variables are variable, they can be modified. Constants are constant, the idea is to never modify them!
Also, connect this block with other block (for example "Pass"). If a block is not connected, it is not used at all.