I have a 1990 300E 3.0 BENZ.

Would you please instruct me as to the correct procedure
for removing the black leather gear shift knob.

On the W124's and the W201's the gear selector (automatic) is one piece and "lock" bolt fastened under the center console. You need to carefully pry up the console wood cover. Disconnect the switches on the cover and lift out of the way. Unscrew the PRDNL plate and that will expose the lock nut at the base of the shaft. Going to need a skinny wrench to loosen the nut then you can twist and an unscrew the shaft.

BTW, if you want to replace the one piece knob with a two piece (shaft and knob), there are adapter shafts for $15, then you can choose the later model MB knobs or aftermarket knobs.