I’ve seen one of these be installed, also 40 ft tall, for fixed wireless internet. Once it was up right and ready, a guy climbed up and installed the dish.

He had a basic climbers harness around his waist and legs, and attached to that, 2 more strands of harness on his left and right, with a large carabiner clip on the end of each. He’d unhook then rehook the carabiners one by one, then climb higher. When he was at the top he used both of them to kind of give himself a makeshift seat he could lean back into, freeing up both his hands.