Clean that part of the screen. Clean it again - and maybe once more for luck.
Clean the part of the stalk that sticks to the screen, make sure it's well and truly clean & grease free.
The pad will work best if the screen & mirror stalks are warmed up first.
I could never understand the thought processes behind sticking a mirror to the screen. Only ever had one car where the mirror was screwed to a housing on the roof.
On the plus side, if you are a tall driver (like me), the ability to reposition the whole mirror is a bonus.