If motor is bad and you need worm you cut shaft off motor and press out remaining shaft. Or have a fixture to support worm while removing shaft with press. That is how I do it. If motor is good and the worm is bad I cut a slot down the worm without going into the shaft. Use a dremel with wheel. The worm will usually split and press off easy. Otherwise you damage motor thrust assembly.
Pressing on require solid support of the shaft at flywheel end to press new or old worm on.
Make sure you have a measurement of where the worm need to be seated. G
