Look at a shop manual and get some tools. You'll have to take the engine off the frame. You'll have to take the engine cases apart to get at the transmission.This is a pretty involved job. The transmission is not separate. All you can probably get at if the clutch and carburetor without removing the engine from the frame. Any Honda shop should be able to take care of this quickly. They'd probably laugh with glee to get such a small job. Your CT70 is worth fixing, if it can be fixed.