u have to get the hm water fall that he dropped then give it to him but he lets you keep it
When you beat snorlax
First you have to go to the radiotower and battle team rocket.
You need HM07 to teach your Pokemon the move "Waterfall" which allows he/she to swim up the obstacle to the other side. The HM can be found by talking to the man on the "Ice Path".
Just keep moving forward. Talk to the old man to get one of the HM's you need. As for the boulders, you just need to move them into the closest hole and bounce off of them on the ice in the floor below the rocks.
Hidden Power? Once you get through the Firey Path, there should be a guy standing in front of a tree. Talk to him and he'll give you it. From then on you can buy it from a man in Slateport Market.
Between Route 44 and Blackthorn City is a cave with four floors called the Ice Path. On the 1st Floor of the Ice Path, on the other side of the third path of ice you will find HM07 Waterfall. _____ First go to blackthorn city, once you've complete the gym go to the right path, keep going and enter the cave ice path, go until you find a big patch of ice that takes a while to pass, rocks on each side of path way you need to go to, go right after that, you will have one more thing to do and at the end of it will be HM 07 the waterfall move. You can also just keep on going until you see a man that won't let you by (in the cave) and you have to get his HM he dropped and then go to talk to him and he will tell you to keep it!
in the ice path if you miss it an old man should stop and tell you about it
you will have to find the man in ice path talk to him and then he will give you hm water fall
Get the national dex
you have to clear team rocket from the goldenrod radio tower before the man will let you pass
you have to go to the radio tower and stop team rocket from capturing it.
When you go through ice path, halfway through there will be a man asking you to retrieve his item on the other side of a patch of ice. Get it for him and he will let you keep it: HM waterfall!