You align the processor on the board. It has a recess in one corner which I have always marked white. I also made a white dot on the board before desoldering.
Now the processor has to be aligned so that all pins are on the right solder pads, that's a fumbling.
Then I always soldered the pins in the corners first to fix the processor.
Here I show you the soldering technique with which I achieved the best results. I have neither added new solder nor flux.


Then check for solder bridges or unsoldered legs. To do this, set the multimeter to continuity test, so that a sound is heard when the test probs make contact.