Usually just running the pump with normal water is enough, if during extraction you water is flowing very slowly, it means your coffee is either too fine, and the water pressure is not sufficient or you tamped your coffee too much with the tamper. I would experiment with first reducing the amount of pressure applied when tamping, if that doesn’t work, try reducing your coffee dose by a little, if it still doesn’t work, you need to grind your coffee a little more coarser.
