I've not swapped a bezel on a 9300 yet, but on a regular Speedmaster Professional, the movement has to be in the case while you press the bezel on, because you need the dial in place to line up the bezel properly. So I do that with the watch fully closed up. The 9300 may have some other method of alignment, but don't put too much faith in the red dot - it is just a drop of model airplane paint, and can be accidentally removed just by handling the watch.
Cheers, Al
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