I wanna make auto double pump in Fortnite

[begginner]

I wanna make a script that switch slot to second pump gun(slot number 4) after clicking LMB (shot) and back to first pump gun (slot number 3) after clicking again LMB (shot).

Also i would like to turn this script by XButton1.

I tried do something but nothing worked. Please help me

[norisk]

XButton2::
^XButton2::
+XButton2::
Send {3}
Sleep 500
MouseClick ,Left,X,Y,3,0
Send {4}
Sleep 500
MouseClick ,Left,X,Y,3,0
return

[awe]

How do i do that? where do i put it?