Coolant on the ED's is not a recommended service item shown on the service sheet at all. That coolant is not working very hard, so Mercedes basically says leave it be. I don't think I've heard of anyone on the forum changing the coolant on an ED. I am anal about maintenance on my cars and flush the coolant every three years on my ICE vehicles whether they need it or not, but have no plans to touch the coolant on my ED's.
2014 EV Coupe 16,500 miles
2014 EV Cabriolet 6,500 miles