I have learned to add solder to the existing joint on the motor wire on the main board before I start to unsolder it, and that sometimes helps soften the OEM "high melting point" solder that DJI uses. If you need to add solder, use thicker solder, it melts slower and is a little easier to work with. Thin gauge solder sometimes sizzles and splatters tiny droplets of solder in unwanted places on the motherboard that could short out other components.
The key is in the iron that you use. A while ago, I was using a Weller solder station, but that didnt get hot enough, and I had to leave the tip on the solder joint a little too long for comfort, at the risk of damaging the main board. It was ok for microsoldering.
Now when I solder, I use the 2 second test. If my iron doesnt break a solder joint loose in 2 seconds or less, I raise the iron temp.