This process is both difficult and time-consuming. Take your time and be extra careful not to overheat the solder pads or pins. Avoid using desoldering wick to desolder the leads, as it could easily destroy the pads.

Press the tip against another solder pad and feed the solder wire into the heated area until there's a small solder joint on the pin.

Check if any solder unintentionally bridged with a different joint. If so, carefully use your iron to heat the solder between the joints and separate the bridge. If the bridge doesn't want to separate, desolder it using a desoldering pump and try again. Be careful not to overheat the pins or the pads while desoldering.

Repeat this process for all of the remaining microcontroller pins.