On your app, click on App and select OnStart and then create a variable as hideLabel and set it to true
OnSelect function of your button create a variable and set it an if statement.
If(hideLabel, false, true)
And on your label's Visible function remove true and set it to hideLabel variable. So each time when you click on your button if hideLabel is true it will set it to false and hide your label, if it is false it will set it to true and display your label.