okay you have to defeat the team rocket in goldenrod city
Defeat team rocket
Mahogany town
it is in between Mahogany town and Ekruteak city
catch entei and raikou
on the route between mahogany town and blackthorn city
fly to mahogany town and go west
get to mahogany town
After you beat pryce in mahogany town
You can find the TM Thief in the Team Rocket hideout in Mahogany Town.
past the rage candy bar dealer in mahogany town (right of the town) to the ice cave
You meet him at the lake of rage after fighting or catchig the red gyrados.
You go to one of the houses in Mahogany Town and then you will find stairs and team rocket.