We also had to replace a couple of spring leaves just last week.
Jack it up by the frame. Support the axles so that they are not hanging by the shiocks or brake wires. Remove the wheel with the broken spring.
Easiest to remove the entire spring stack to work on it. There is a locating bolt that goes through the center & keeps the stack together.
As long as you have everything apart might as well replace spring hanger bolts with wetbolts. Another thought. RV builders are notorious for building to minimum spec. Probably why the spring broke. Too much weight for too little spring. A one leaf upgrade with longer U bolts might be worth doing all round.