It will push out, its simply being difficult. There is a ring cut into the trigger pin. The slide stop fits into this ring. You need to center the slide stop and then push out the pin. Push the pin out left to right so you dont have to hassle with the ring more than once.
Be sure to give the slide stop the "flick test". Once the trigger pin is installed flick the slide stop upward. If it does not spring back into place the slide stop spring slipped out above the trigger pin. You will have to remove the TP and reinstall