@kinghnvn ,
You cannot reset the concat() function result unless you empty the collection selectedDesks.
If you don't want that you can use a context variable emptyMyLblDesk in OnSelect property of the Back Button:
UpdateContext({emptyMyLblDesk:true})
set the Text property of the LblDesk control to:
if(emptyMyLblDesk,Blank(),Concat(selectedDesks,Title&", "))
and OnVisible property of the screen change the emptyMyLblDesk value to false:
UpdateContext({emptyMyLblDesk:false})
Hope it helps !
