Change button title

You should create a Bool State var that holds the condition to choose between X and Y.

@State private var buttonXCond = true  // toggle to false when needed

Then in Button, have a conditional Label:

               Button {
                   // The action
                   }
               } label: {
                   Text("\(buttonXCond ? "X" : "Y")")
               }

Is it UIKit or SwiftUI ? For SwiftUI, see previous post.

For UIKit:

          myButton.setTitle(buttonXCond ? "X" : "Y", for: UIControl.State.normal)