HOW TO AUTOMATICALLY BUY STOCK WHEN THE PRICE DROPS BELOW A CERTAIN POINT?

How do we automatically buy batch when it drops the sure price?
The past couple of days bonds have left up the lot as well as I hold the little have been overpriced. I consider the couple of of the ones I wish will go down in cost as well as which when I wish to buy it though I won’t be during the mechanism for many of monday as well as tuesday. I was wondering if there is the little approach which I can set the cost which I hold it will go down to as well as afterwards automatically squeeze it?