SHIA Railink
This link
https://railtravelstation.com/tag/shia-railink/ provides more detailed info and pics. Note that the first part covers a trip from the city to the airport, and the second the other way.
It also gives this heads up: “Get on the SHIA Railink to try out the service if you must, but in the long run, unless the train is the destination like on this trip, and taking into account the first mile/last mile connectivity, the hassle to purchase tickets and the overall fare, I’ll be sticking to the cheaper and faster DAMRI Airport Bus.”