My experience tells me that
1/ don't keep the wild yeast unfed for several days.
2/ to eliminate the sourness, feed the basic yeast with equal portion of water & flour
i.e. if the base is 200g, then feed 100g flour & 100ml water and let them ferment.
3/ reduce the fermented time, you may put the dough in the oven preheated with a
bowl of hot water.
4/ keep feeding the yeast everyday.