I'm assuming that you have beaten the elite 4 and lance the pokemon league champion. If not then that is what you have to do first of all.
If you have then you should be given a cruise ticket by either professor oak or elm then you use that ticket to travel from Johto to Kanto and work your way from saffron city to either pallet town or to pewter city. A shortcut to pewter city would be the tunnel leading away from saffron city but it is blocked by a sleeping snorlax but if you have the radio card in your pokegear then you can wake it up to catch it or just make it faint its at level 50 and has leftovers (meaning it can heal itself when you attack).
If you have done all of this then all you need to do is head into the indigo plateau building but go towards mt silver then I beleive you can fly to Kanto. An even easier way would be to get the rail card by helping to restore power to the power station in the Kanto region.
If you have then you should be given a cruise ticket by either professor oak or elm then you use that ticket to travel from Johto to Kanto and work your way from saffron city to either pallet town or to pewter city. A shortcut to pewter city would be the tunnel leading away from saffron city but it is blocked by a sleeping snorlax but if you have the radio card in your pokegear then you can wake it up to catch it or just make it faint its at level 50 and has leftovers (meaning it can heal itself when you attack).
If you have done all of this then all you need to do is head into the indigo plateau building but go towards mt silver then I beleive you can fly to Kanto. An even easier way would be to get the rail card by helping to restore power to the power station in the Kanto region.