## behold a man full of leprosy was there ##
The word "behold" alerts us to a new person in the story. Your language may have a way of doing this. English uses "There was a man who was full of leprosy."
## he fell on his face ##
"he bowed down to the ground" (UDB) or "he knelt and touched the ground with his face"
## implored him ##
"begged him" or "pleaded with him" (UDB)
## if you are willing ##
"if you want to"