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Ken I may know who to contact to answer this question. Standby…

Shower drains drop in from the top of the tub or shower base. Typically a thin rubber gasket is between the drain and the shower pan.  Old one needs to be removed first.  Depending on your model you need to gain access by removing the felt covered wall in the basement. Usually a Hepvo drain or a P-trap that needs to be removed first. Loosen the slip nuts and lower the tail piece from the drain. Probably need a second person to hold the drain piece from turning by sticking a needle nose pliers down in the drain fitting to keep it from spinning while the nut underneath is loosened and removed. Remove drain piece. Clean surface for replacement drain and do the reverse and put it all back together.  Shouldn’t be too tough to figure out.