A soldering iron isn’t going to get the job done for high density BGA packages. Example chip:

All those dots are balls of solder. The chip needs to be placed on the board in exactly the right position and orientation, and then the whole thing placed in a reflow oven so that the solder balls can melt and flow appropriately without bridging any connections.

Doing this at home without the right tools is essentially impossible. With the right tools, it’s merely quite difficult. Reflow soldering takes experience and carries the risk of damaging other components on the board which may not survive the temperatures in the reflow oven, so need to be removed first. Plus the reflowing procedure itself is guided by a temperature profile which would have been developed through experience in the factory with specific adjustments for the thermal characteristics of this board. Get the profile wrong and you may break other connections when the solder fails to flow, or have other chips on the board come loose.