Remove the plastic belly pan yourself, it is held on with four 10 mm
bolts.

Then yes, remove the lower radiator hose to let it drain out.

There is another drain plug to open, on the passenger side of the
engine block, toward the rear, near the bottom of the block: takes two
different sized wrenches to loosen it (bigger diameter wrench on
inside, against block to hold it in place; smaller wrench outside,
next to it, to turn and loosen the stopcock.

Huh? Why would anyone with any inclination to work on their own car pay
a mechanic to perform such a simple task? It's easy enough to pull the
splash pan, drain the coolant, flush it out and then fill it up with a
50/50 mix, anyone with basic hand tools can do it.