Google maps will have you walking miles along road to motorway overpass then up roads to get here.
Easist and quickest is by tunnel in KLSentral. We’re KLIA train exist are stairs to the right of welcome to KL sign. You will require a train pass? as are gates to get through. Go up stairs and just keep going till the end were you can exit up some stairs, you are now at KL station exit. Facing road go right not left as map would indercate. Approximately 50 meters down road look for a tunnel to your right about 25 meters away, going through here you will come out at the botanical garden lake. Look out for guy driving a electric cart thingy. For a small fee he will take you to the buttifly and bird parks.